Vardenafil, a potent and selective phosphodiesterase 5 inhibitor, has entered phase 3 clinical trials. Pharmacodynamic studies showed that the maximum plasma concentration after oral administration of 20–40 mg of vardenafil occurred in 0.7–0.9 h, the half-life was 4–5 h, and negligible amounts remained in the circulation after 24 h. The efficacy of vardenafil compared with placebo was shown in RigiScan studies, a phase 2 study involving 601 men with mild-to-severe erectile dysfunction for at least 6 months, and a phase 3 study involving 452 diabetic men. Adverse effects were not severe and tended to decrease with time.