Normal men and normally menstruating women received i.m. injections of 0.1 to 4.0 mg/kg sulpiride. This psychotropic drug induced a very rapid (already significant after 5 minutes) and sustained (still significant after 7 hours) elevation of prolactin (PRL) concentrations in all subjects with no consistent modification of LH and FSH. After injection of 4.0 mg/kg, there was similarly no modification of mean TSH concentrations in the women tested in the luteal phase, as well as of mean GH levels in men. Sulpiride prevented the inhibitory effect on PRL levels of 500 mg levodopa, administered orally simultaneously; levodopa administered 2 hours prior to sulpiride failed to counteract the PRL-stimulatory effect of sulpiride. Under chronic sulpiride-induced hyperprolactinaemia, levodopa exhibited however a very slight inhibitory effect on PRL concentrations. These data are in agreement with the hypothesis that sulpiride acts mainly at the pituitary level by blocking dopamine receptors of the lactotropes and support the concept that the menstrual cycle perturbations observed under chronic sulpiride administration result from hyperprolactinaemia itself or from a mechanism quite similar to that by which sulpiride induces hyperprolactinaemia.