The results presented herein establish a definite antispasmodic effect of a purified alkaloid of P. affinis (APA) and agrees with the previous findings of Barros et al. (1970), with the crude extracts. APA was found to depress spontaneous activity in intestinal, uterine and vascular smooth muscle, and in cardiac pacemaker and myocardial tissue. Similarly, it blocked cholinergic activation of intestinal smooth muscle and skeletal muscle and adrenergic activation of the rabbit uterine smooth muscle. APA did not block caffeine induced contracture in frog rectus abdominis or reverse Ach contracture after it had been induced. These findings give evidence of the cell membrane as the site of action of APA.