The excretion of the hallucinogen dimethyltryptamine (DMT) and its precursor N-methyltryptamine (NMT) was studied among 74 recently admitted psychiatric patients and 19 normal persons. Both compounds were detected in 24-hour urine samples from all subjects. Dimethyltryptamine excretion was greatest in schizophrenia, mania, and "other psychosis" and tended to decline as clinical state improved. Psychotic depressives excreted smaller amounts of DMT more akin to those excreted by neurotic and normal subjects. Urinary NMT excretion was unrelated to psychiatric diagnosis. Ratings on the Present State Examination (PSE) also indicated that increased excretion of DMT was associated with psychotic rather than neurotic psychopathology. Forty-three percent of the variance in urinary DMT levels could be explained in terms of six of the 38 PSE syndromes. Syndromes suggesting elation, perceptual abnormalities, and difficulty in thinking and communicating were most correlated with raised urinary DMT excretion.