MELBOURNE, Australia: A new trial at the Royal Children's Hospital here hopes to demonstrate the effectiveness of the anti-depressant Zoloft - which can help to control obsessive-compulsive disorders in adults - in treating Asperger's syndrome.

Simon Dafter, who has Asperger's, has his sights set on becoming a policeman, or perhaps building a town. When he was about three, his mother, Trisha, noticed a sudden, distinct change in his personality. "He'd been a lovely, placid little boy and he just started getting stubborn," she said.

Children with Asperger's, like Simon, are often intellectually very bright, but have difficulty seeing how certain behaviour affects other people, and they tend to have a narrow set of interests.

Dr John Mathai, a child and adolescent psychiatrist who is directing the new trial at the Royal Children's Hospital, said he hoped Zoloft would help control repetitive and aggressive behaviour. The hospital already has 10 children on the trial, but hopes to recruit up to 60 children, aged seven to 15. Half will be given the drug and the other half will not.

"What we expect to see is that the children on the active drug ... will be improving their social relationships and be more manageable," Dr Mathai said.

It is believed about one in 500 children has Asperger's syndrome. Simon is not on the trial but has been taking another anti-depressant for two years, which, his mother said, had had a positive effect. "He's a lot calmer, you can reason with him, he's not as aggressive."

"Much less aggressive," agreed Simon. Now he's doing more school work, instead of tearing up pages, as he once did.

Simon, too, is a fan of the new medication. "They work really well, make me feel much better, more co-operative, more agreeable," he said.

Simon's real passion is science - last year he gained a high distinction in a national science competition. So when offered the chance of a tour of the labs at the hospital, he wasn't about to knock it back. "Yes!" he said excitedly. "You won't be able to stop me!"