On the basis of reports describing nitric oxide as a form of endothelium-derived relaxing factor and on our own experience with intracavernous use of nitric oxide-releasing substances in animal models, we undertook an approved human study of intracavernous sodium nitroprusside as a treatment for impotence. We report our early experience in which severe hypotension and only mild tumescence in our first 3 patients caused us to discontinue the trial.