Some doctors who believe that the components of childhood vaccines, such as mercury, have been responsible for many cases of autism advocate detoxification programs in which children take chemicals that bind with metals in the body and force them out through urine. Others promote gluten-free diets under the theory that autistic children have high levels of a certain type of yeast in their digestive tracts. And then there are the proponents of HBOT, which has gained a following among parents who claim it has helped children with neurological problems, including cerebral palsy, traumatic brain injury, encephalitis and, most recently, autism.

Inside an office in an industrial section of Honolulu is the Hyperbaric Medicine Center. The first stop on the tour by Maryellen Markley, its patient care coordinator, is in front of two color brain scans that she said show the profound results of HBOT. The first scan, she said, reveals that an autistic child had decreased blood flow and profound neuro-inflammation before the oxygen therapy.

"Look at how much has changed in the second scan," Markley said, pointing. "Better blood flow, less inflammation, more connections between the two sides of the brain. This child, a 6-year-old, was completely nonverbal since the age of one-and-a-half, and after 66 hours of hyperbaric oxygen therapy was talking again."

Markley said she has treated more than 30 autistic children with HBOT and "every single child ... had consistent quality-of-life improvements." The improvements, she said, were more pronounced in kids most afflicted by the characteristics of autism: the repetitive behaviors and the impairments in sensory perception, social interaction and communication.

Critics argue that no studies have been done that use scientific models such a double-blind testing. They caution that the treatment has been tried only on a handful of autistic children nationwide, not nearly enough to draw valid conclusions.

"They are making extraordinary claims without extraordinary evidence," Iyama said.

Evidence is exactly what supporters of HBOT are hoping to get in the coming months. Beginning in May, the Honolulu clinic, along with about 20 hyperbaric oxygen clinics across the U.S., will launch a formal study into how autistic children respond to the therapy. About 400 children will be studied, and the results are to be evaluated by the National Institutes for Health.

Other studies are under way. One of the biggest is a federally funded study on the effects of HBOT on children with cerebral palsy at Wright-Patterson Air Force Base near Dayton, Ohio.