A study was undertaken to determine the incidence of increased serum levels of human prolactin (hPRL) in women during oral contraceptive therapy, and to correlate this with both the dose of oral contraceptive medication and the duration of its use. The 123 patients in this study were divided into 3 groups according to the dosage of estrogenic component of the combined oral contraceptives. Thirty percent of these women had hyperprolactinemia of varying degree. Neither the dosage of steroids within our range nor the duration of therapy correlated with the presence or degree of hyperprolactinemia. The actions of estrogen-progestin compounds on hPRL are discussed.