A limited literature is reviewed concerning plant sources of substituted tryptamine alkaloids, the uses of these plant materials as hallucinogens by primitive peoples and the occurrence of tryptamines as urinary metabolites in human subjects. Certain aspects of the psychopharmacological and biochemical characteristics of 5-methoxy-N, N-dimethyltryptamine (5-MDT) are presented and the possible role of this substance as an endogenous psycho toxin in schizophrenia is discussed.