The present study provides information on differences in the gastrointestinal microflora of children with autism compared with a control group. Special attention was paid to the microbiological characteristic of the new obligate anaerobic microorganisms: Clostridium bolteae sp.nov. and Cetobacterium somerae sp.nov. observed in stools of children with autism. In light of recent publications, the hypothesis of interactions between intestinal microflora - and the brain based on possible alterations in bacterial toxins and other metabolites in the pathogenesis of autism is discussed.