DMT is one of a number of substances which have been from time to time considered as a cause of schizophrenia. Our laboratory is interested in DMT because an increase in DMT synthesis is consistent with a deficiency of monoamine oxidase. While a deficiency of monoamine oxidase has been found in some patients with schizophrenia, to date only blood platelets have been found deficient, and whether the deficiency is more generalized remains unknown. Nevertheless, an examination of whether DMT could fit a number of required criteria for serious consideration as a schizophrenogen seems warranted. DMT does appear to fit at least several of the criteria. In single dosages it is capable of producing at least some schizophrenic-like symptomatology. It and its precursor can be found in human tissue, and the enzymes for DMT synthesis are present in man. In several species tolerance to repeated administration has not been found to develop. The most significant piece of negative evidence is the failure to find elevated DMT plasma concentrations in schizophrenic individuals, but in retrospect the extremely short in vivo life of DMT suggests that it might be metabolized too quickly to be able to use blood concentrations to differentiate schizophrenics and normals. Urine appears to provide an even poorer measurement. Even those criteria that are met at this point are met only in a small number of experiments. It would seem that DMT remains a candidate' for the causative agent for at least some schizophrenias.