Penodynamics, the functional evaluation of erection after intracavernous injection of vasoactive drugs, is a simple screening test that excludes significant vascular problems if full erection occurs within a reasonable period of time. Although it is more invasive than the penile brachial index (PBI), it is well tolerated and easy to perform. There is good evidence that studies on the flaccid penis are less accurate and do not correlate well with the results of functional papaverine testing. To evaluate arteriogenic impotence, sonography and pulsed Doppler analysis combined with papaverine injections provide objective and reproducible measurements of diameter increase and blood flow of each penile artery and have the advantage of being a functional study. Although this equipment is expensive, it is available in many centers where noninvasive vascular flow studies are performed. With training, the technique can be mastered by anyone. The arterial response to papaverine and the resulting erection allow indirect judgment about the venous system. Therefore, the whole penile vasculature can be evaluated with this technique. Currently, many drugs or drug combinations are used to induce artificial erection, not only for diagnosis but also as a therapeutic alternative to penile prostheses. The only physiologic agent is prostaglandin E1, a substance that seems to be as effective as papaverine but can be metabolized within the cavernous tissue and reportedly results in fewer incidences of prolonged erection and priapism. The use of vasoactive drugs is also very helpful for angiographic studies by improving flow and diameter of the penile vessels, which will result in better images of the arterial lesions.(ABSTRACT TRUNCATED AT 250 WORDS)