Recent studies from our laboratory have investigated the hormonal response to various forms of sexual stimulation, including film, masturbation, and coitus in both men and women. This series of studies clearly demonstrated that plasma prolactin (PRL) concentrations are substantially increased for over 1h following orgasm (masturbation and coitus conditions) in both men and women, but unchanged following sexual arousal without orgasm. Here we discuss evidence suggesting that the PRL response to orgasm may play an important role in the control of acute sexual arousal following orgasm. Supporting this position, chronic elevations of PRL (hyperprolactinemia) produce pronounced reductions in animal sexual activity, and significant reduction of libido and gonadal function in both men and women. These data suggest that PRL may represent a peripheral regulatory factor for reproductive function, and/or a feedback mechanism that signals CNS centres controlling sexual arousal and behaviour. Thus, we propose a theoretical model of the role of PRL as a neuroendocrine reproductive reflex.