Apart from heads spinning in 360-degree circles and streams of flowing green vomit, real-life exorcisms are remarkably similar to what you see in the movies, an Australian exorcist says.

Father Barry May - an Anglican priest, exorcist, author and former police chaplain - has performed dozens of exorcisms in his 40 years of ministry.

The 73-year-old Perth man says more Australians are seeking exorcisms, and as such, over the past four years he has dedicated his life solely to ridding people of their demons.

Father May tells anyone sceptical about the ancient Catholic ritual to "get real" and psychologists have backed the man, saying exorcism "has its place" in society.

"I've been spat at, yelled at, grabbed at, sworn at, had people trying to rip my crucifix off my throat, gouge my eyes out, fighting, assault. I get all that stuff and you tell me it's superstition?" Father May said.

"No, get real. And that's exactly what it is, it's real.

"Forget the head spinning and the green vomit you see in the movies, but the rest of what you see in the movies is damn close to being real, it's not funny.

"It takes a lot out of me, I sweat profusely. It's a real exercise-and-a-half I tell you."

Father May says his first calling into the world of demons came in the 1970s when a woman at a funeral he was conducting asked him if he believed in ghosts.

"I thought it was a rather strange question to ask," he said.

"I told her 'yes', and she said 'well I've got a ghost in the house next door to me'. So I went to her house and dealt with it."

Since then he has developed an expertise in exorcism - casting the "evil one" out of people - and is approached by hundreds of people each year who claim to be possessed by a demon - or two.

"I remember I did one with a girl who was about 23 years of age and I kept saying to her 'are you free yet?'.

"And she would say 'no I'm not', in her own voice.

"It took hours and hours to deliver her and as soon as I said 'spirit, reveal yourself', she would growl and spit and cross her eyes.

"She threw about 12 of the demons out and she was free."

The Catholic Church's Lismore Bishop, Goffrey Jarrett, says Catholicism recognises various forms of exorcism.

He says they were first performed by Jesus Christ.

"Minor exorcism ordinarily takes place in many of the church's rites and sacraments, using the sign of the cross, and in the blessing of people and material things such as holy water," he said in a recent statement in response to the increasing number of requests for exorcisms.

"Major exorcism, however, may be required in rarer cases where it is established by appropriate investigation that the victim's claim to be tormented by a demon is really true."

Father May says he performs both types of exorcism, but major exorcisms are his specialty. He says the ritual requires a crucifix, candle, holy water and most of all, a commanding voice.

But he says he will only perform one if, after several interviews and meetings with the person, he deems them to be possessed, rather than psychologically ill.

"I might see somebody every two weeks but generally I might have only done 20 exorcisms in my life," he said.

"The ancient rite of exorcism is only used after a lot of investigation and the person needs to agree to it... not everybody has demons. I think that's a mistake people make."

In a successful exorcism, Father May says the demon is sent straight to hell. But he says there is always the risk it will inhabit another person in the room.

"About 10 years ago I had a lady who was very erotic, getting on her hands and knees - I won't go into the details on that - but she was making barking noises, thrusts with her body, it was just ghastly to watch," he said.

"I had her husband there with me - thank goodness. But I cast this thing out of her, and then on the other side of the curtain this bloke started doing the same thing.

"He started barking and yelling and shouting and screaming, it was just a ghastly experience."

Father May says one of his worst experiences has been with women and men who claim to have been raped by demons while lying in their beds at night or watching TV.

"It's rather a mystery because although intercourse doesn't take place they feel as though it has. They feel absolutely ravished and raped, and several women have had that problem," he said.

"I've had two men tell me they've had that same problem with female demons who try to have sex with them."

Lismore's Bishop Jarrett puts the issue down to "a widespread preoccupation with Satanism and various occult practices", and Father May agrees.

"People are messing around with stuff they don't know," he said.

"They're not all crackers, they're not all psychos, they're those ordinary people who live in our streets, they've done something they shouldn't have done and they've got their fingers burnt."

Demon versus state of mind

Psychologist Dr Mitch Byrne from the University of Wollongong says while he does not believe in demons, the method of exorcism has its merits.

"Oddly enough, I'd say yes there is a place for these people," he said.

"If you are a person who is possessed of a delusional belief or a psychiatric disability, and you have a strong religious belief, and that belief can be marshalled to help you overcome your distress then why not?"

"I wouldn't say it is the best call or should be the first call in terms of a way of dealing with psychological disturbance, but people should never underestimate the power of belief.

"Suicide bombers and Kamikaze pilots are evidence that the power of belief is beyond any sort of rational argument, so perhaps working within someone's belief system is the best way to help them recover from their disability or distress."

He says he has no doubt people who believe they are possessed do incredible things, but he attributes this to the mind - not demons.

"There is an enormous amount of power and energy in the human body that we don't usually exert, and people under the right sort of circumstances can marshal that power for a very brief and short period of time, usually at some physiological cost," he said.

"They can marshal it to engage in acts of human strength and agility and so on.

"So if a person is possessed of a delusional belief or a psychotic condition they may evidence some degree of excessive or unusual behaviour which we might interpret as being possessed or as evidence of a demon."

Dr Gerard Stoyles, also from the University of Wollongong, is both a psychologist and a Catholic priest.

Unlike Dr Byrne, Dr Stoyles believes in the existence of demons, or an "evil presence", as he describes it.

He says there is a place for exorcism provided all other possible psychological, psychiatric and medical conditions have been ruled out.

"As a psychologist I'd have to say that somebody who is giving out all the indications of being evil and bad... I would not automatically say that person is possessed," he said.

"My first inclination would be that this person has somehow gone right off the rails.

"But I believe also that there are instances where people can end up being caught up in behaviours that are outside the realm of the normal, that they don't want, are not conscious of, that are not like them personally, and for which there is no explanation either in the physical world or in the world of medical and psychological and psychiatric science.

"Once you turn around and say there is no scientific explanation for this person's behaviour... then you're confronted with the question of what the hell is it?"

Dr Stoyles says too often, people seeking exorcisms are not given proper medical treatment.

"I get very concerned when people are denied good physical, psychological and psychiatric treatment simply because someone is convinced that they are possessed and therefore they must go down this route of exorcism and ignore the route of medical care," he said.

"That is just playing a game with people's lives, so it angers me and it concerns me.

"This issue is something that has to be very, very carefully addressed with a rational and scientific mind that seeks out what is really going on rather than what is exotic and what is fantastic... I think too much of that sort of stuff goes on."