It is only 9:30am but already the donor cabins at the Cryos sperm bank are in demand.

There are three in total.

Each contains a washbasin, some pornographic magazines and a television, if you prefer your entertainment on the screen.

"And you have pornography here too," I say, gesturing awkwardly towards a sketch of a naked woman hanging on the wall in one of the cabins.

"Oh, that's not pornography," says Ole Schou, the director and founder of this booming business.

"It's just a nice picture."

He is right of course and it is that kind of straight-talking that has helped him create this little empire of sperm production in Aarhus, Denmark's second largest city, but still with a population of only 250,000.

It all began, so the story goes, when he had a dream more than three decades ago about frozen sperm.

A painting depicting Ole Schou's dream about sperm. ( Supplied )

Adorning the walls of the clinic are paintings of this dream, an artist's impression of it.

They defy description.

The men who come here to do their business spend little time admiring the wall-hangings.

They hurry past the reception, pick up a container from a drawer just outside the donor cabins and head in.

A red light signals the room is occupied, for as long it takes.

It feels inappropriately intimate to be standing just metres away from the donation rooms, but that is what we do for a while, because at one point all three are occupied and we have to wait to go and film one from the inside.

By this time it can barely be 10:00am.

"It's not usually this busy," says Anders, a 42-year-old who has agreed to speak to us about why he donates sperm here.

He says he is motivated by a combination of wanting to help people, wanting to leave behind something of himself in this world, and the money he is paid to deliver samples.

Tens of thousands of potential babies

How much you get varies depending on how good your sample is.

That is decided straight away, after you come out of the cabin and hand back your little jar to the receptionist.

The sperm clinic lab is right behind the reception desk and Ole Schou proudly takes us on the tour.

Straws of sperm at Cryos. ( Supplied )

The sample is first analysed through a microscope.

Deciding how good the sperm is, is pretty straightforward.

To simplify it grossly, if there's movement, it's good.

Sperm samples are siphoned into small tubes, called straws, and placed in a huge vat for cooling.

At the time we visit there are around 30,000 samples in one of these vats.

"Making material for thousands of children," Mr Schou says.

From there the sperm is packed into small tanks and sent off to clinics and individual women around the world.

"There's increasing numbers of home inseminations or do-it-yourself," Mr Schou says.

Donor motivated to help people

Back out at reception we meet another donor, Jacob, a panel beater who is currently out of work and who, like Anders, sometimes comes to the clinic several times a week to donate.

He also says the money is important, but that was not the initial reason for signing up.

He says he and his girlfriend wanted to have a child but had difficulties conceiving, so went to a clinic for tests.

It turned out there was nothing really preventing his girlfriend getting pregnant, in fact Jacob tells me his sperm count was really pretty good, it just took a while.

Jacob says he likes helping people by donating sperm. ( ABC )

They now have a baby girl, but the 33-year-old says he got a sense of what it felt like to want to have a child and not be able to.

He says it was a hopeless, horrible feeling.

"People take it for granted," he said.

"You know, that you can go out and get drunk and sleep with somebody and you're pregnant … but it's not that simple."

Jacob's girlfriend actually encouraged him to become a sperm donor.

Around 50 per cent of Cryos's clients are single women, like Georgie Ogilvie-Jones from Shropshire in England.

"I never met the right guy," she says.

"So ultimately it had come to the point where it was now or never just biologically and I decided to go for it."

Her baby, Freya, was born last July, conceived from sperm from Cryos.

Georgie and her daughter, Freya. ( Supplied )

Accessing sperm in the UK was hard, because like many countries including Australia, men can no longer donate anonymously and that has seen donor numbers fall significantly.

"I liked the idea of a little Viking, however silly that sounds," Georgie says.

Denmark still allows men to donate anonymously, but both Anders and Jacob have chosen to allow their details to be accessed once any child born from their sperm turns 18.

Jacob tells me he made the decision to be non-anonymous because he felt if he found out he had been conceived with donor sperm he would like to meet his biological father.

"I would die to," he says.

It is well into the afternoon by now and time is pressing, because the clinic closes at 5:00pm and we have to get some more vision of the laboratory before the technicians go home.

Jacob and I wrap up our interview and he casually pops over into a cabin to give a donation.

No point, I guess, in turning up at the clinic just to give an interview.

All the same I'm glad I have made my exit by the time he re-emerges.

Watch Barbara Miller's report on Lateline tonight at 9.30pm (AEDT) on ABC News 24 or 10.30pm on ABC TV.