Penile erections were regularly induced by intermittent subcutaneous injections of apomorphine in five patients with Parkinson's disease (PD) complicated by motor fluctuations. Four of the patients reported erectile dysfunction before beginning apomorphine and two of these report a significant improvement in their sexual function resulting from apomorphine use. Animal studies suggest central D2-type dopamine receptor stimulation and oxytocin release from the paraventricular nucleus of the hypothalamus mediate the effect. Erections reported with other dopamine agonists and levodopa are probably mediated by the same mechanism. Apomorphine-induced erections in PD are probably more common than previously thought. The benefit of apomorphine on sexual function in some patients suggests a possible role in the treatment of impotence in PD.