This study examined the effects of previous ovarian surgery on the clinical response to ovulation induction with clomiphene citrate-human menopausal gonadotropin in an in vitro fertilization program. Patients were divided into five clinical groups: group A (n = 63), no previous ovarian surgery; B (n = 9), unilateral cystectomy; C (n = 6), unilateral oophorectomy with no contralateral ovarian surgery; D (n = 7), bilateral ovarian surgery with both ovaries present; and E (n = 4), unilateral oophorectomy and contralateral cystectomy. Patients in group E demonstrated significantly lower serum estradiol on cycle days 9-11 (P less than or equal to .05) and fewer follicles on cycle days 11-12 (P less than or equal to .05) than did patients in groups A-D. The percentage of cancelled cycles increased with increasing amounts of ovarian surgery (P less than or equal to .03). The study suggests that one cause of a poor response to ovulation induction for in vitro fertilization may be prior extensive ovarian surgery.