AIM: To study the effects of exogenous excess of testosterone on the constricting effect of phenylephrine and endothelium-dependent and -independent relaxing effects of different:agonists in the corpus cavernosum penis (CCP). METHODS: Specimens of the CCP were obtained from rabbits testosterone for 1 and 2 months and untreated for 2 months after testosterone-treatment for 2 months. Preparations were mounted between two parallel platinum electrodes in organ baths. Responses to phenylephrine, car bachol, and:sodium nitroprusside were obtained by adding the reagent cumulatively to the bath. RESULTS: The phenylephrine-induced contractions were decreased with no change in agonist potency (pD(2) value) after both 1 and 2 month testosterone-treatment and did not return to control: values in corpus cavernosum obtained from rabbits untreated for 2:months after testosterone-treatment for 2 months. Testosterone treatment for 1 or 2 months increased the endothelium-dependent relaxations induced by carbachol and decreased the relaxations elicited by electric stimulation but did not affect the relaxations induced by sodium nitroprusside. These relaxant responses to carbachol and electric stimulation did not return to control values in corpus cavernosum obtained from rabbits untreated for 2 months after testosterone-treatment for 2 months. There were no significant changes in the pD(2) values calculated:by agonist-induced relaxation responses in all tesrosterone-treatment.