An animal model was developed to elucidate the effect of chronic obstruction of the internal pudendal artery on the responsiveness of the corpus cavernosum. In male albino rabbits, the internal pudendal artery was chronically ligated unilaterally with a silk tie and the occlusion was maintained for 1 month. The control group was sham-operated. The reactivity of corpus cavernosum tissue from the ligated animals and the control animals was studied in organ chambers. Unilateral chronic ligation of the internal pudendal artery caused an impaired contractile response to alpha-adrenoceptor stimulation with decreased Em and pD2 values and an impaired relaxant response to electrical field stimulation but resulted in a marked increase in the endothelium-dependent relaxant response to carbachol with an increased pD2 value. However chronic obstruction of the pudendal artery had no effect on adenosine-, papaverine- and sodium nitroprusside-induced relaxant responses, and there was no change in agonist potency. These data indicate that altered penile hemodynamics have an effect on the reactivity of the corpus cavernosum and may contribute to the etiology of impotence.