Prolactin (PRL) response to an intravenous administration of metoclopramide (10 mg) was examined during normal pregnancy and puerperium. Basal PRL and the metoclopramide-induced increase of PRL increased gradually during pregnancy. This was paralleled by serum estradiol, estriol, and progesterone levels. A positive correlation between serum progesterone and metoclopramide-induced PRL concentrations was found at week 36 of pregnancy. In lactating women, metoclopramide always induced higher increases of PRL than did suckling stimulation on the seventh day postpartum. The PRL responses to suckling and metoclopramide were significantly correlated with each other, but no correlation was found between placental steroid levels throughout pregnancy, PRL levels after parturition, and total milk production during seven days postpartum.