Bufotenine (BUTN) is a hallucinogen with psychotropic effects. High levels of BUTN and its precursor, N-methylserotonin are shown for the first time to occur and to accumulate mainly in the brain during the degradation of serotonin in the central nervous system of the toad, Bufo bufo japonicus. These compounds are concentrated in the hindbrain, which includes the cerebellum and medulla oblongata. BUTN can also be detected in blood and urine specimens from the toad. In humans, autism is a subtype of schizophrenia that appears to be a functional disease of the brain. BUTN can be detected in urine specimens from infant autistic patients. Analysis by three-dimensional HPLC suggests that the presence and levels of BUTN may be important markers for the diagnosis of autism. It appears, therefore, that some aspects of the central nervous system of Bufo may provide useful pharmacological clues to the etiology of human psychiatric diseases, such as autism, that are known to be linked to the methylation of serotonin.