through regulation of pain receptor expression and secretion 32 of neurotransmitters. The gut microbiota comes into contact with metals and other contaminants as they are ingested through dict. It is likely that 33 microbes are presented with metals in water and food and may play a role in protecting the host from metal adsorption. Micro- bial sequestering of heavy metals by the intestinal microbiota is strongly supported by studies that show that when these con- taminants are consumed at much higher concentrations, there is a lower detection in clinical samples, excluding absorption and dilution factors 34.3s Mechanisms for the binding of metals to bacterial cell walls include ion exchange reactions with peptido- glycan and teichoic acid, precipitation through nucleation reac- tions, and complexation with nitrogen and oxygen ligands 36-38 Since we found that copper levels, but not zinc levels, are lowered when associated with probiotic therapy, s in microbiota change may selectively affect the absorption of copper. The dynamics of this will need to be elucidated with future studies. There were limitations to this study. We were unable to differentiate effect of different types of probiotics. This was based on varied therapy and the number of individuals in our study. Also, we did not follow individual patients, but the data represent a comparison of individual MPO levels, patients who had not taken probiotics with those who received the therapy. We did not find a relationship between length of probiotic use and MPO levels (unpublished data) These data strongly suggest that autistic children taking probiotics have significantly lower levels of MPO and copper. It is possible that altered gut flora, because of probiotic ther- apy, results in less inflammation, which, in turn, results in lower MPO levels. Lower copper levels may also be the result