Effects of mazindol on the contraction induced by nerve stimulation and agonist drugs were investigated to examine the inhibition of catecholamine uptake by mazindol in the vas deferens. Mazindol at 10^-9-10^-7M potentiated a single electrical pulse-elicited neurogenic contraction which consisted of a twitch and phasic contraction. This potentiation was almost completely antagonized by prazosin. Mazindol leftwardly shifted the dose-response curve to norepinephrine in a dose-dependent manner ; the dose-ratio was 6.2-fold and 83.2-fold at 10^-9M and 10^-7M mazindol, respectively. The dose-response curves to dopamine and methacholine were also slightly shifted by mazindol. In the dibenamine-treated vas deferens, mazindol did not affect the dose-response curve to methacholine. These results suggest that mazindol potently inhibits the norepinephrine uptake without acting on the smooth muscle cells in the rat vas deferens.