A simple sniffing test could determine if children have autism even before they are able to speak, researchers say.
People spend longer smelling pleasant aromas such as flowers than sour smells such as rotten food.
But researchers in Israel found during a recent trial that children with autism generated an "inappropriate" sniff, spending the same amount of time smelling each opposing aroma.
The results, published in the Current Biology journal, showed that the more severe the symptoms of autism, the longer the children inhaled the unpleasant smells.
Researchers believe it could provide a crucial indication for autism in non-verbal children, who are usually diagnosed from the age of two, and help them to receive early behavioural interventions.