Hi Jim, 
I found the study. It was published in 2000.  The citation is: 
Sandler RH, Finegold SM, Bolte ER, Buchanan CP, Maxwell AP, Väisänen ML, Nelson MN, Wexler HM. Short-term benefit from oral vancomycin treatment of regressive-onset autism.  J Child Neurol. 2000 Jul;15(7):429-35.
and you can read the abstract at: 
http://www.ncbi.nlm.nih.gov/pubmed?term=short-term%20benefit%20from%20oral%20vancomycin%20treatment%20of%20regressive-onset%20autism

80% of the 12 children in the trial showed rapid and significant improvements following a course of Vancomycin. The particular strain of clostridia produces a neurotoxin called proprionic acid. Unfortunately, it is highly resistant to antibiotics and develops spores that will regenerate after the removal of the antibiotic. Sure enough, when the Vancomycin was discontinued, the clostridium returned and so did the symptoms of autism.  It is pretty compelling evidence that the many cases of autism are the result of gut bacteria. It also suggests why a gluten free, dairy free diet produces a remission in symptoms because the gut mucosa provides a much better barrier with removal of these foods. I suspect that there is a similar dynamic with other strains of gut bacteria in ADD and other brain disorders. 

Best Wishes, 
Ron
_________ 

Interesting.  I am fairly well convinced that autism is caused by  
gluten and is the extreme of a spectrum shared by ADD and other  
disorders of the brain.  Can't see how gut flora might fit into that  
picture.

Jim