Owing to the vasoconstrictive effect of nicotine, smoking may potentially interfere in the results of the drug-induced erection test for papaverine hydrochloride. To investigate the effect of smoking on this test, 12 patients between 22 and 65 years old underwent the following protocol: phase 1--intracavernous injection of 100 mg. papaverine hydrochloride with measurement of intracavernous pressure by puncture with a 19 caliber butterfly needle attached to an aneroid manometer and phase 2--1 week after the initial test the procedure was repeated after the patient smoked 2 cigarettes. In phase 1 all men obtained a full erection, compared to only 4 in phase 2. The average intracavernous pressures were 85.83 and 53.50 mm. Hg, respectively, in phases 1 and 2 (p less than 0.01). We conclude that cigarette smoking, probably through nicotine, interferes with the drug-induced erection test, which might explain some false negative results.