The "love hormone" oxytocin alters the brain activity of children with autism and makes them more social, according to US researchers.
The role of the hormone in helping children with autism has been debated, with studies showing conflicting data.
Brain scans, reported in the Proceedings of the National Academy of Sciences, hint that there is an effect.
The National Autistic Society said research on oxytocin as a treatment was still in its infancy.
Oxytocin is naturally produced by the body, triggers labour and is involved in mother and baby bonding.
Seventeen children with autism, aged between eight and 16, were given two nasal spray - one containing oxytocin, the other no drugs at all.
After taking each one, the impact on brain activity was recorded in a scanner while the children were shown "social" pictures of human faces or "non-social" pictures of cars.
The parts of the brain normally associated with social situations appeared more active after the children had been given oxytocin.
One of the researchers, Prof Kevin Pelphrey, told the BBC: "We are very excited by the findings, all 17 showed a response, although the response was variable.
"There's still lots of questions about oxytocin, but this suggests it enhances social brain functions and decreases non-social functions - helping kids to focus on socially relevant information."
Larger trials are taking place to see what the side-effects and benefits of oxytocin might be in children with autism.
Exactly how the drug should be used is still up for debate, with some suggestions that it would be best used as an aid during current behavioural therapy rather than as a daily medication.
Prof Pelphrey said some parents were giving the drug to their children without medical advice and this was a "terrible idea".
"It might have no effect or it might cause damage," he said.
However, he added: "The most exciting finding is not oxytocin, but that you can show changes in the brain by a compound.
"It changes how we think of autism and how treatable it might be."
Carol Povey, director of the National Autistic Society's centre for autism, said: "Research investigating the impact oxytocin can have on people with autism is still in its very early stages.
"While the findings of this particular study are interesting, no hard and fast conclusions should be drawn.
"Autism is a very complex disability and can present a variety of challenges that extend beyond social difficulties.
"It's crucial that those living with the condition have all their needs assessed so that they can access the appropriate support."