The neuroendocrine response to sexual activity in humans is characterized by a pronounced orgasm-dependent increase of plasma levels of prolactin. In contrast to the well-known inhibitory effects of chronic hyperprolactinemia on sexual drive and function, the impact of acute prolactin alterations on human sexual physiology is unknown. Therefore, this study was designed to investigate the effects of acute manipulation of plasma prolactin on sexual behavior. Ten healthy males participated in a single-blind, placebo-controlled, balanced cross-over design. Prolactin levels were pharmacologically increased to high levels (protirelin, 50 micro g i.v.) or reduced to low physiological concentrations (cabergoline, 0.5 mg p.o.). Sexual arousal and orgasm were then induced by an erotic film and masturbation. In addition to continuous neuroendocrine and cardiovascular recordings, the quality and intensity of the acute sexual drive, arousal, orgasm and refractory period were assessed by extensive psychometric measures. Administration of cabergoline decreased prolactin levels and significantly enhanced all parameters of sexual drive (P<0.05), function (P<0.01) and positive perception of the refractory period (P<0.01). Administration of protirelin increased prolactin concentrations and produced small, but not significant reductions of sexual parameters. The sexual effects observed from cabergoline were completely abrogated by coadministration of protirelin. Although different pharmacological sites of action of prolactin-altering drugs have to be considered, these data demonstrate that acute changes in prolactin plasma levels may be one factor modulating sexual drive and function. Therefore, besides a neuroendocrine reproductive reflex, a post-orgasmic prolactin increase may represent one factor modulating central nervous system centers controlling sexual drive and behavior. These findings may offer a new pharmacological approach for the treatment of sexual disorders.