In summary, following their intraperitoneal administration, 5-methoxy-N,N-dimethyltryptamine and N,Ndimethyltryptamine were excreted rapidly in the urine. Despite the high rates of excretion, only a very small percentage of the administered dose appeared in the urine unmetabolised. An examination of the metabolic profile in urine led to the identification of a number of characteristic metabolites. Of these, the N-oxides were of the greatest quantitative significance. The excretion profiles of the Noxides indicated that these metabolites were also subject to rapid excretion. Pretreatment of animals with the monoamine oxidase inhibitors resulted in a marked increase in the percentage of the administered dose appearing in urine as either the parent compounds or their N-oxides.