One of us (H .T.) has developed sensitive and reproducible modifications of methods for detecting indoleamines in human urine by the paper and thin layer chromatographic techniques . Using these modifications and also the recently developed gee-liquid chromatographic methods of Capella and Hornine, we confirmed the presence of bufotenin in the urine of each of four achizophrenic patienta examined when they were receiving traaylcypromine, a monoamine oxidase inhibitor, both with and without the simultaneous admiaiatratioa of cyeteire . Without the MAO inhibitor, the excretion of bufotenin was estimated as being leas than 1 ug per day. In the presence of MAO blockade, the amounts of urinary bufotenin were established as 4-10 ug per 24 hours, one-half in the free and ore-half in conjugated forms . Increases of urinary excretion of bufotenin were observed about two weeks before the mental symptoms of these schizophrenic patients worse red and these increases continued during the period of behavioral exacerbations .