The lack of unchanged DMT in the urine suggests that the breakdown process in man is similarly rapid as has been shown in rats. The very rapid metabolism of DMT may be the explanation for the short duration of the psychosis. The quick onset and the above-mentioned short duration is a new feature in contrast to the hitherto used psychotics as meskalin, LSD-25, etc. These latter substances produce their psychotic effect only 1-2 h after the administration. The enrichment of the excreted urine in 5-HIAA after the administration of DMT is a very interesting fact.There are two possible mechanisms to explain this elevation. Either DMT, or its breakdown products, were oxydated at the 5-position of the indol nucleus to produce 5-HIAA, or the endogenous Serotonin were metabolized to a greater degree. The latter possibility seems to be the more probable one, but this ought to be proved by radioactive, isotope-labelled DMT. This would provide further support for the hypothesis of BRODIE et al that Serotonin plays an important role in brain function.