Plasma prostaglandins F2 alpha and E (PGF2 alpha, PGE) and urinary PGE were measured in 10 women treated with human gonadotropins (HMG) and subsequently with human chorionic gonadotropins (HCG). Five women became pregnant (6 pregnancies). There was no correlation between concentrations of plasma PGF2 alpha or PGE and plasma estradiol or progesterone. Urinary PGE concentrations showed a positive correlation with estradiol before HCG and a negative correlation with progesterone after HCG, only in women who subsequently became pregnant. Higher urinary PGE concentrations before HCG suggest that either HMG or rising estradiol levels stimulate PGE renal production. The significant negative correlation between urinary PGE and progesterone concentrations, after HCG, in those patients who became pregnant suggests that ovarian production of progesterone may decrease renal production of PGE.