In addition to tryptamine and serotonin, we found bufotenin (5-hydroxy-N,N-dimethyltryptamine) both in free and conjugated forms in the urine of four schizophrenic patients under dietary control when they were receiving tranylcypromine, with or without cysteine loading. The amount of bufotenin was estimated to be as little as 4-10 microg. per 24 hr. urine; one-half in the free, one-half in the conjugated form. In the absence of monoamine oxidase blockade bufotenin was also excreted in some patients, but less than 1 microg. per day. N-methylserotonin, N, N-dimethyltryptamine and 5-methoxy-N, N-dimethyltryptamine were also disclosed, but only by thin-layer chromatography and especially when the patients were receiving tranylcypromine with or without cysteine. Increases of urinary bufotenin and other N-methylated indoleamines were observed about two weeks before the mental and behavioural symptoms of the schizophrenic patients worsened, and these elevated levels continued during the period of behavioural exacerbations.