Julia Roberts as the female lead? John Candy as a mad German? John Belushi in outer space? Those were just some of the things that could have made the iconic movie a whole lot different.

In the early 1980s, Ivan Reitman got a call from an old friend, Dan Aykroyd, who wanted to talk about a 70-page movie treatment he had written, inspired in part by his father and grandfather's fascination with the supernatural.

Aykroyd — whose dad wrote the book A History of Ghosts and whose granddad tried to make contact with spirits through radio waves — had set his story in the future, largely in outer space. It was a wild, chaotic symphony of brilliant ideas, centered on two men to be played by Aykroyd and John Belushi. But in those days long before CGI, not all of his notions were filmable, let alone dramatically coherent.

Over breakfast at Art's Deli in Studio City, Calif., Reitman, the director of such hit comedies as 1979's Meatballs and 1981's Stripes, told Aykroyd that the story would work much better if it were set in the present day and in a city like New York. Aykroyd, who had worked with Reitman in Canadian television, readily agreed, and the director signed on to make the movie.

That was the beginning of Ghostbusters, the 1984 film that has become a comedy classic. It was also the beginning of a frenetic race to make the picture in little more than a year after Columbia Pictures" Frank Price greenlighted it for $30 million without knowing anything except its title, its premise and its stars.

Bill Murray had already signed on when Reitman boarded the project; but Belushi's death of a drug overdose in 1982 meant the cast had to be rethought, as well as the plot.

Over a couple of weeks, two writers, Aykroyd and Harold Ramis, huddled with Reitman in Martha's Vineyard to craft the script, even as the director was searching for someone who could handle the movie's massive special effects, and Columbia's board pondered whether it had committed a terrible mistake in betting so much money on a comedy.

When the picture opened in June 1984, it proved a sensation. It spawned a sequel, a whole new genre of FX comedies, and the current reimagining, the new Ghostbusters that is opening today, which Reitman produced with Amy Pascal.

In his own words, Reitman tell the inside story.

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Dan Aykroyd wrote a 70- or 80-page treatment called Ghostbusters, a two-hander for John Belushi and himself. It was about two or three years before I ever got involved, but it never got made because, unfortunately, John passed away. It sat on a shelf somewhere, and Aykroyd may have spoken to other actors, but I'm not aware of it. There are some rumors that he had a conversation with Eddie Murphy about it, but we never really discussed that, so I don't know.

He finally had a conversation with Bill Murray just after I did Meatballs and Stripes with Bill. Bill thought it was a good idea, and Aykroyd called me and said, "Once you read this, tell me what you think." And I read it.

It took place in the future, mostly in outer space. There were competing groups of ghostbusters; it seemed to be a common profession. And there were all sorts of extraordinary apparitions and monsters. It was a remarkably complicated sci-fi movie that would be hard to do today, never mind back in the pre-CGI era.

I thought Danny had created a genius idea, it just wasn't set right. So I invited him to breakfast at Art's Delicatessen in the [San Fernando] Valley. I knew him: When I'd just started working in Toronto, I did some television [game show] on a budget of $500 a week — no exaggeration — and Aykroyd was the studio announcer.

I said, "Look, I love this idea that there are people whose job is to catch ghosts and act like firemen. But it should have a contemporary setting, a big city that we know, like New York. There's something [better] about seeing apparitions in a context that we understand, like in our living rooms or on our city streets, rather than in a void in outer space in the future sometime."

He said, "That's cool."

Reitman, far right, directs a scene from the 1984 Ghostbusters.

And I said, "Actually, the story of their formation would be good." And I pitched this idea that these guys were paranormal investigators — like, looking at paranormal studies at a university in some kind of postgraduate study program. They get in trouble, they get kicked out, and then they fortuitously set up a business. That was what I pitched at this breakfast and he said, "That's all cool."

He was very, very generous with me, but he's known for that and he just wants what's best for his stories.

I also suggested bringing Harold Ramis in. Harold and I had worked together, starting on [1978's] Animal House, and I brought him in to Meatballs, had him co-star in Stripes. I thought he would be able to execute my point of view more clearly than Aykroyd could in terms of the tone that I thought would be necessary. And Danny loved this idea.

Within a week I was in [Columbia Pictures president] Frank Price's office — it was just Frank and Marvin Antonowsky [Columbia's head of marketing]. Frank had bought Stripes on a pitch and it turned out really well, and now this was going to be the next movie, he thought.

So he said, "What do you want to do?" And I pitched Ghostbusters in much the way I'd pitched it to Aykroyd at the breakfast, and he said, "Wow, that sounds great. How much do you think it will cost?" Stripes had cost $10 million, and I said, "Maybe three times as much." I just pulled a number from the air and said, "$30 million."

He said, "OK, you got it."

I said, "You mean you're greenlighting this?"

He said, "Yeah. You make it for $30 million. It's Bill and Danny and Harold, right?"

I said, "Yep."

And he said, "The only restriction is, you have to deliver it ready for theaters on June 8, 1984."

This was May 1983, so we had 13 months from that meeting. There was no script, no effects house and no starting date.

About three weeks later, the Ramis family, the Reitman family and the Aykroyd family all went to Martha's Vineyard. We had three separate homes that we'd rented. Danny actually had his own house; he'd been living there. We all would meet every single day in his basement. And basically we wrote Ghostbusters together. It was really a nonstop enterprise over a two-and-a-half-week period.

We were meeting about six hours a day, and the guys would go off and write on their own for about four or five hours a day. And then I would bring it in and I would do a polish and we would pitch new ideas to each other. We'd have combined family dinners, but everybody understood we had to get a usable document by the time we left there a week after the July Fourth weekend.

[The hardest part of the writing] was figuring out, what's really going on? What's the bad guy doing? Who is the bad guy? How do these ghosts manifest themselves? The biggest leap for me was the concept of the Marshmallow Man, which we took from Aykroyd's original treatment. It was one of many elaborate creatures in his treatment. But there was just something special about it that tickled me. But over the course of the writing, it was always the thing I was the most worried about. [Up to the point in the story when the Marshmallow Man appears] we're dealing in relatively believable storytelling. But a 110-foot Marshmallow Man walking down Central Park West? That's something else.

Aykroyd, Murray and Ramis with Reitman on the Ghostbusters set.

The Marshmallow Man was the same [in the final film] as it was in the initial concept. Dan had a friend who had done a rough sketch of this goofy Marshmallow Man, and he also had this "No Ghost" stop-sign symbol. Michael Gross, who worked with me as a producer and was one of the former art directors of the National Lampoon magazine, cleaned up that "No Ghost" symbol to what it is now, but that's the genesis of one of the most famous trademark icons in the world.

We were in a constant hurricane, just trying to get everything done. There was only one big visual effects house and that was ILM [Industrial Light and Magic], and Steven Spielberg had already booked it for Indiana Jones and the Temple of Doom, so they weren't available. Everybody else was too small for the job. We had something like 630 [effects shots]. But there was Richard Edlund, who had done Star Trek. I thought, "Let's hire him and build a company around him." So I got Columbia to advance $5 million to Edlund to set up his own company, to buy the equipment that was necessary.

This all happened literally while we were writing the script in Martha's Vineyard. Frank Price just believed in this idea and stood up for it.

[When it came to casting], the biggest castmember to find was the part of Dana Barrett, and a number of people came in. Julia Roberts was one of the first. I thought she was spectacular and I turned to my casting director, saying, "She's going to be a big star." And then Sigourney Weaver walked in.

Now, Sigourney was slightly older, had just done [1979's] Alien and she was so smart about the script. She said, "You know, I really think that Dana Barrett should be possessed. She should be like that dog on the roof." And then she got on all fours on my coffee table, howling like a dog!

She was funny and had a regality, and having her with my Ghostbusters was like having Margaret Dumont with the Marx Brothers. Right after she left my office, I called Harold Ramis and said: "Harold, Sigourney Weaver just started howling like a dog in my office. She said that she should get possessed by the dog and turn into a dog," and I thought, "Damn, that's a really good idea." We had been having all this trouble about how to handle what happens on the roof in the last act, and we hadn't solved it. Her idea of being possessed really personalized the larger concept — and that got included in the script. She was barely out of my office and we were writing it already.

I'd worked with John Candy on his first American film, Stripes, and I sent him the script and said, "I think I've got something really great for you." It took him a couple days before he called back. He said, "I'm not sure I'm getting it." I said, "What do you mean?" He said, "I don't see the character. Maybe if I played him with a German accent, he'd be funny. And I could have a couple of German shepherds." There were these two dogs already and I thought, there's too many dogs. He finally passed. Then Rick Moranis read it and called me and said, "Look, just between you and me, John Candy is an idiot. This is an amazing part and I know exactly what to do." He was an extraordinary addition.

I had now directed two movies with Bill Murray and I knew what that experience was going to be like, just how much he brings to the table on a daily basis. The problem with Bill was [pinning him down]. He'd been shooting in France, and I remember Danny and I going to JFK and picking him up to make sure he was on the plane.

The first day that Bill arrived, we picked him up, threw a costume and a backpack on him, and he came out on the street with the other guys. I had them walk down Madison Avenue as if they were running toward something, and we started shooting. It was the first shot we ever shot, and they looked so good. Even before the cameras rolled, I got this shiver down my back. I said, "I think we're going to do something special here." It was like a premonition.

We started shooting in New York sometime in the middle of October 1983. We shot there for six weeks solid, and I loved shooting in the city. It was much easier than it is now. They let me close down major avenues, [though afterward] there were reports that some kind of terrible earthquake happened on Central Park West.

I had a mechanical effects crew that was second-to-none, because we ended up having to do a lot live on camera. The card catalog scene in the library was done live. I remember bringing my young son, Jason, who was then about 5 — he's become quite a good filmmaker — to the set. He was usually bored watching his dad work, but on that day he just freaked out when all the card catalogs started flying. The first thing he said was, "Wow, that's so neat! Do it again!'

The card-catalog scene was all compressed air. Air and strings. We only did about three takes, and I had three or four cameras: one right on the cards in close-up, one on [the librarian] reacting to the cards flying around her; and a couple of big wide shots. I conducted it like a musical piece: each [card catalog that burst open] had a number, and I remember calling, "One, four, two," and the cards would come flying out.

We shot in New York for six weeks, then just before Christmas we flew to Los Angeles and started filming there between Christmas and New Year's and all the way through January. We shot at the Burbank Studios and built a huge set.

[The toughest part was shooting] everything on the roof, because it was hot and it was a combination of visual effects, comedy and scale. We built this high platform, and just to climb up and move all the cameras was complicated.

[Production designer] John DeCuir Sr. created this extraordinary practical set, and we shot there on this large stage doing the rooftop sequence. We'd never do this today — I mean, everything else would be done CGI or greenscreen. But he painted this huge 360-degree backdrop that went around this large stage. We had painters paint the city of New York, and there were bits of lights attached to it so that things would twinkle in the far distance, and we even added little planes and models on wires to animate the backdrops.

To light it we needed pretty well every big electrical fixture in the city, and about four generators added to all of the studio power. While we were shooting, no other production could go at the Burbank Studios because we were using all of the electricity that was available.

The whole shoot was about 62 days, which was kind of remarkable. We finished shooting at the end of January 1984. Sheldon Kahn, my editor, had a cut three weeks after we completed shooting. He'd send me black-and-white sequence reels as we were shooting, because I knew we were going to be really under the gun getting the movie ready for the June 8 promised date. I had to hold up my end of the bargain with Mr. Price. I was cutting while we were shooting and that was very helpful, because I got into a real sense of what the rhythm and pacing should be.

In a strange way, it was not strenuous. I've had much harder shoots that kept me up. This one was touched by angels. The great thing is, I was working with these comedy geniuses, the most brilliant, funny people in the English language.

Three weeks after we completed shooting, I had Columbia Pictures recruit 200 people off the street to see this movie called Ghostbusters. I thought, "Screw it, let's just show the movie with very few visual effects shots and see if the story works.'

We showed it on the lot; they had a nice little theater on the second floor. I got up in front of the audience and said, "Look, one day there'll be a lot of special effects in this film and none of them are done, but I think you're going to get it.'

It was extraordinary. They started laughing and applauding. When [Weaver] opens up her fridge, we didn't have anything to show there, so we just said "shot missing," and the audience went crazy. We only had two or three shots of the Marshmallow Man, mostly close-ups of the head — because it was really a guy with a rubber head over his own head, shot against miniatures. They started screaming and applauding as soon as they saw the head in its very first close-up. That told us that we didn't have to worry.

Ghostbusters opened at No. 1 and stayed No. 1 every single week of that summer in 1984 except for one, when a Clint Eastwood film [Tightrope] knocked it to No. 2. It dethroned Animal House as the No. 1 comedy up to that point.

It was a helluva ride.

Reitman, Murray, Ramis and Weaver during the filming of the 1984 Ghostbusters.