A double-blind, partial crossover study on the therapeutic effect of yohimbine hydrochloride on erectile dysfunction was done in 82 sexually impotent patients. All patients underwent a multifactorial evaluation, including determination of penile brachial blood pressure index, cavernosography, sacral evoked response, testosterone and prolactin determination, Derogatis sexual dysfunction inventory and daytime arousal test. After 1 month of treatment with a maximum of 42.0 mg. oral yohimbine hydrochloride daily 14 per cent of the patients experienced restoration of full and sustained erections, 20 per cent reported a partial response to the therapy and 65 per cent reported no improvement. Three patients reported a positive placebo effect. Maximum effect takes 2 to 3 weeks to manifest itself. Yohimbine was active in some patients with arterial insufficiency and a unilateral sacral reflex arc lesion, and in 1 with low serum testosterone levels. The 34 per cent response is encouraging, particularly in a Veterans Administration population presenting with a high incidence of diabetes and vascular pathological conditions not found in regular office patients. Only few and benign side effects were recorded, which makes this medication worth an attempt, often as a first line of treatment even at a dose of 8 tablets.