We have analyzed products of the serotonin-degradative pathway, in which both N-methylserotonin and bufotenine are formed in urine specimens of products with psychiatric disorders by three-dimensional HPLC with electrochemical detection. Bufotenine was detected in urine from all autistic patients with mental retardation and epilepsy (n = 18) and many autistic patients (32/47) with mental retardation. Bufotenine was detected in the urine of 15 of 18 patients with depression. Thirteen of 15 schizophrenic patients were also positive for bufotenine. N-methylserotonin was also detected in some cases of each disorder. Only two of 200 urine specimens from healthy controls were positive for bufotenine. Thus, the presence and levels of bufotenine might be useful and important markers of some psychiatric disorders.