The excretion of dimethyltryptamine (DMT) was studied amongst 122 recently admitted psychiatric patients and 20 normal subjects. DMT was detected in the urine of 47% of those diagnosed by their psychiatrists as schizophrenic, 38% of those with other non-affective psychoses, 13% of those with affective psychoses, 19% of those with neurotic and personality disorders and 5 % of normal subjects. Ninety-nine patients were interviewed in a semi-standardized fashion, and also categorized according to a variety of operational definitions of the psychoses. The operational definitions failed to reveal arty group significantly more correlated with urinary DMT than a hospital diagnosis of schizophrenia, but a discriminant function analysis of symptomatology could be used to define a group of 21 patients of whom 15 (71%) excreted detectable DMT. There was a general relationship between psychotic symptoms and urinary DMT, but specifically schizophrenic symptoms did not appear to be major determinants of DMT excretion.