['To determine whether angiotensin-converting enzyme (ACE) inhibition would affect ovarian steroid synthesis in the oocyte donors undergoing controlled ovarian hyperstimulation (COH).', 'The IVF program of the University of Southern California.', 'Prospective matched clinical trial.', 'Twelve oocyte donors were studied in 28 hyperstimulation cycles.', 'Donors underwent a standard COH protocol. Follicle aspiration was performed 34 hours after administration of hCG. After the procedure, seven donors were administered the ACE inhibitor, captopril, 6.25 mg orally twice daily for 4 days. The remaining patients served as controls.', 'Serum E2, P, plasma prorenin, active renin, and angiotensin II (Ang II).', 'Angiotensin II increased after aspiration in both groups but was significantly lower in those receiving captopril. Peak P in the captopril group was significantly lower than controls (81.8 +/- 27.8 versus 208.5 +/- 23.9 ng/mL [conversion factor to SI unit, 3.180]). Peak E2 was significantly higher (2,222.4 +/- 875.3 versus 425.6 +/- 490.4 pg/mL [conversion factor to SI unit, 3.671]). Active renin and Ang II correlated with P.'] Does angiotensin-converting enzyme inhibition reverse luteal phase steroid production in oocyte donors?