The aim of this study was to investigate the effect of sertraline, a selective serotonin re-uptake inhibitor, on contractile responses to noradrenaline (NA), KCl, serotonin (5-HT) and electrical field stimulation of rat isolated vas deferens. 2. Pre-treatment with 10(-4) M sertraline showed inhibitory effects on responses to NA, KCl, 5-HT and electrical field stimulation, while pre-treatment with 10(-6) and 10(-5) M sertraline caused potentiation of responses to NA (10(-7) and 10(-6) M). 3. A voltage-dependent calcium channel activator, Bay K 8644, restored the inhibited responses when sertraline was washed out of the organ bath, although restoration could not be seen when sertraline was not removed. 4. The inhibition of the contractile responses by sertraline pre-treatment may be via a mechanism through calcium channels which is additional to the selective serotonin re-uptake inhibitory effect of sertraline.