Using c-propyldopacetamide (H 22/54), a tryptophan hydroxylase inhibitor, and c-methyltyrosine methylester (H 44/68), a tyrosine hydroxylase inhibitor, the effects of 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) on amine turnover in central 5-HT, NA and DA nerve terminals of the rat were studied using histochemical fluorescence methods for the demonstration of CA and 5-HT. It was found that 5-MeO-DMT in single or repeated doses of 5 mg/kg decreased the H 22/54-induced disappearance of 5-HT fluorescence in 5-HT nerve terminals and increased the H 44/68 and H 22/54-induced disappearance of NA fluorescence in NA nerve terminals, suggesting that 5-MeO-DMT decreased 5-HT turnover and increased NA turnover. In the functional experiments, 5-MeO-DMT markedly increased the extensor hindlimb reflex of the spinal rat independently of presynaptic 5-HT stores, a reflex which is highly dependent on 5-HT receptor activity. These results suggest that 5-MeO-DMT can directly stimulate central 5-HT receptors. It is proposed that the decrease in 5-HT turnover observed is secondary to the 5-HT receptor stimulation induced by 5-MeO-DMT, which elicits a negative feed-back resulting in a reduction of the activity of the 5-HT neurons. In view of previous studies on d-LSD, dimethyltryptamine and psilocybin (Anden et al., 1968, 1971) and the present results, a capacity to stimulate 5-HT receptors seems to be a common property of hallucinogens of the indolealkylamine type. Keywords : 5-Hydroxytryptamine Catecholamines Extensor reflex 5-Methoxy N,N-dimethyltryptamine Histochemical amine analysis Amine turnover