Sitting in hot water for half an hour temporarily made children more sociable and less prone to repeating the same action over and over again.
The same researchers also showed that a dose of parasitic worms helped some adults with the condition.
It is hoped that the unusual approaches will increased understanding of the autism and speed the search for new treatments.
More than one in 100 British children has autism or a related condition such as Asperger’s Syndrome - a ten-fold increase on 30 years ago.
Symptoms vary from child to child but they usually revolve around difficulty with social interaction, difficulty with communication and a need for routine and repetitive behaviour.
Patients are usually treated through a combination of speech, behavioural and other therapies.
Although drugs can be given to control symptoms such as aggression or hyperactivity, there is no cure.
The hot bath experiment was inspired by the observation that in up to a third of cases, the symptoms of autism are eased when a child has a fever.
To find out more, the U.S. researchers asked ten autistic children in whom this had been seen to sit in baths of two different temperatures and asked their parents and a doctor to assess their behaviour.
Sitting in water of 39C (102F) for half an hour produced a noticeable improvement in the ability to communicate and a reduction in repetitive behaviour.
However, a bath that was just two or three degrees cooler had no effect, the American College of Neuropsychopharmacology’s annual conference heard.
The researchers, from the Albert Einstein College of Medicine in New York, are now studying how a higher temperature helps.
One possibility is that it switches on genes that dampen down an overactive immune system.
The second part of the experiment focused on the immune system – and the ability of parasitic worms to calm it down when it has gone awry.
Every two weeks for six weeks, ten adults with autism swallowed thousands of eggs from a worm that normally infects pigs and does not cause illness in people.
While this might sound bizarre, parasitic worms have already been used to successfully treat illnesses in which the immune system turns on the body, including Crohn’s disease.
After the treatment, the adults were more open to new experiences and less focused on following the same rigid routines.
It is thought that the worms triggered the release of chemicals that helped calm the overactive immune system.
Researcher Eric Hollander said that more research is needed – including work on people with more severe forms of autism.
However, worms, or a drug that calms the immune system in a similar manner, could eventually be used as a treatment for autism.
Caroline Hattersley, , of the National Autistic Society, said: ‘This is a very small study so its findings should be treated with caution, and no hard and fast conclusions should be drawn.