This double-blind, placebo-controlled clinical trial of yohimbine hydrochloride included 86 patients with erectile dysfunction and without clearly detectable organic or psychologic causes. The patient group ful®lled all entry criteria; 85 of these could be considered for the Safetyrespectively 83 for the Intention-to-treat (ITT)-analysis. Yohimbine was administered orally in a dosage of 30 mg a day (two 5mg tablets three times daily) for eight weeks. Patients were seen for follow-up after four weeks' treatment, and for a ®nal visit after eight weeks.Ef®cacy evaluation was based on both subjective and objective criteria. Subjective criteria included improvement in sexual desire, sexual satisfaction, frequency of sexual contacts, and quality of erection (penile rigidity) during sexual contact/intercourse. Objective criteria of outcome were based on improvement in penile rigidity determined by use of polysomnography in the sleep laboratory. Overall Yohimbine was found signi®cantly more effective than placebo in terms of response rate: 71 vs 45%.Yohimbine was well-tolerated: Only 7% of patients rated tolerability fair or poor, and most adverse experiences were mild. There was no serious adverse event.