Plasma prolactin, progesterone, and 17 beta-estradiol were measured by radioimmunoassay in 58 patients with complete moles, 17 patients with partial moles, and the same number of maturity-matched pregnant control subjects. In both complete and partial moles in the first trimester, the pre-evacuation plasma levels of these hormones were similar to those of pregnant control subjects, but in the second trimester they were all significantly lower than those of pregnant controls. There was no significant difference in the regression patterns of these hormones between complete and partial moles, but the serum beta-subunit of human chorionic gonadotropin (beta hCG) was higher in complete moles. Patients who subsequently developed persistent gestational trophoblastic tumors had higher plasma estradiol, prolactin, and serum beta hCG than those without persistent gestational trophoblastic tumors both before and after evacuation, but the difference in plasma estradiol and prolactin disappeared by nine weeks after evacuation. The levels of these hormones in patients with theca-lutein cysts were higher than those without theca-lutein cysts in the first few weeks after evacuation. Plasma estradiol, progesterone, and prolactin returned to normal nonpregnant levels before serum beta hCG, and they were not useful as tumor markers.