Parents could perform the tilt test, say the researchers
Parents can check whether their baby is likely to have a form of autism by doing a simple test of head movement, say US scientists.
Babies with Asperger's kept their head straight when their body was tilted, the University of Florida team found.
Doing the tilting test in all infants at the age of six months could catch more cases early, they say.
The findings appear in Proceedings of the National Academy of Sciences.
Asperger's syndrome is a form of autism, a condition that affects the way a person communicates and relates to others.
However, people with Asperger's syndrome usually have fewer problems with language than those with autism.
This means the condition often goes undiagnosed for some time.
Autism is usually diagnosed by the time the child is three years old, whereas Asperger's may not be diagnosed until the child is six or seven.
Previously, Dr Osnat Teitelbaum and colleagues found infants who were later diagnosed with autism had shown a host of abnormal movement patterns at an early age.
They set out to see if the same might be true in children with Asperger's syndrome.
They looked at videos of 16 babies and toddlers who had later been diagnosed as having Asperger's.
The infants displayed movement abnormalities comparable to those previously seen in the autistic children.
The infants with Asperger's showed some reflex movements that should have disappeared by their age of development and others that failed to appear.
These included abnormal facial expressions, falling to one side while walking and failing to keep their head in line with the body when tilted.
Although not all of the abnormal movements were present in each of the infants, the researchers believe the tilting test would be a good way to screen for Asperger's syndrome and autism.
They said: "The tilting test should be routinely performed on all infants beginning at six months, particularly if there is a history of autism or Asperger's syndrome in the family.
"This simple, non-invasive test takes 20-30 seconds and can be performed by the infant's paediatrician or parents," they said.
An abnormal result would mean the child would need more testing for the possibility of Asperger's syndrome or other autistic spectrum disorders, they said.
The National Autistic Society welcomed the research.
A spokewoman said: "The earlier a diagnosis is made, the better the chances are of a person receiving appropriate help and support.
"There is evidence to suggest that intensive early intervention can result in a positive outcome for some children."