The dynamics of 17-alpha-hydroxy-progesterone (17-OHP) production during the onset of the luteinizing hormone (LH) surge were evaluated at 8-hour intervals and correlated with plasma estradiol (E2), LH, and progesterone (P) in 22 women superovulated for in vitro fertilization. Plasma 17-OHP levels rose 8 to 16 hours before the earliest rise in LH and P in 18% of patients, but had risen significantly in 82% of patients by the onset of the LH surge. In the late follicular phase, 17-OHP levels correlated significantly with E2 and LH levels, and the number of follicles greater than 10 mm. Because rising 17-OHP levels preceded the LH surge in only a few patients, it has no clinical value as a marker for human chorionic gonadotropin administration for timed oocyte recovery. Plasma 17-OHP levels, however, may complement LH levels better than P levels in determining the most appropriate stage for surge-timed oocyte retrieval.