Breast engorgement and galactorrhea were observed in many patients receiving ritodrine treatment to delay labor due to premature contractions. In an attempt to understand the causes for these phenomena, serum prolactin, progesterone, estradiol and estriol excretion were measured in 11 women. No statistical difference was found in these parameters after ritodrine administration. It can thus be assumed that breast engorgement and galactorrhea after ritodrine treatment are unrelated to changes in these hormones but might be mediated by some other factors or probably by the premature contractions themselves.