To investigate the influence of breast-feeding and prolactin secretion on the pituitary-gonadal function, 3 different groups of patients were studied during the first 8 weeks of the puerperium. Group A comprised patients with hyperprolactinemia and secondary amenorrhea who conceived while on a regimen of bromocriptine. Group B was composed of normal lactating women. Group C comprised nonlactating women treated with bromocriptine. Group A patients had a normal decline in serum prolactin levels during the early postpartum period, but serum prolactin remained completely unaltered after clearance of placental estradiol. In group B suckling increased serum prolactin and suppressed luteinizing hormone. This pattern was not seen in group A. Group C patients had a rapid postpartum normalization of the pituitary-gonadal axis. The results indicate that in relation to lactation the pituitary function is rather autonomous in hyperprolactinemic patients.