The metabolism of 5-methoxy-N,N-dimethyltryptamine-14C has been investigated in the rat after i.p. injection (5 mg/kg). About 59–65 per cent of the radioactivity is excreted in the 24 hr urine, 4–9 per cent is eliminated in the faeces and 1 per cent as carbon dioxide during this time. Of the metabolites appearing in the urine 54 per cent is present as 5-methoxyindoleacetic acid, 9 per cent as bufotenine, 23 per cent as bufotenine glucuronide and 14 per cent as 5-hydroxyindoleacetic acid. Considerable differences in the metabolism occurred at high dose levels. 5-Methoxyindoleacetic acid-3H is not demethylated to 5-hydroxyindoleacetic acid.I.p. administered 6-hydroxy-5-methoxy-N,N-dimethyltryptamine-3H is excreted mainly unchanged and to a minor degree as conjugate and as 6-hydroxy-5-methoxyindoleacetic acid. 5-Methoxy-N,N-dimethyltryptamine is not 6-hydroxylated to a detectable degree in vivo and 6-hydroxylation is apparently of no importance for the psychotropic activity of 5-methoxy-N,N-dimethyltryptamine.