['To determine the levels and pattern of inhibin B secretion during ovarian stimulation in patients with endometriosis and to evaluate the correlation between inhibin B levels and variables of follicular and oocyte development.', 'Retrospective cohort study.', 'IVF center.', 'Women with endometriosis (n = 20) and tubal factor (n = 10) as the only cause of infertility.', 'Inhibin B levels were measured during gonadotropin stimulation on day 1, days 8-11, day of hCG administration, and oocyte retrieval.', 'Patterns and levels of inhibin B secretion were compared in the two groups. Other variables analyzed were age, days of gonadotropin stimulation and total ampules used, oocytes retrieved, and the fertilization and pregnancy rate.', 'Inhibin B levels and number of oocytes retrieved were significantly lower in patients with endometriosis than in the control group. Two patterns of inhibin B secretion were noted: It peaked in the midfollicular phase or on the day of hCG administration. In contrast, E2 levels peaked on the day of hCG administration. Inhibin B in the midfollicular phase in both groups correlated positively with number of oocytes retrieved. In addition, E2 and inhibin B levels in the midfollicular phase correlated positively.'] Is secretion of inhibin B during ovarian stimulation decreased in infertile women with endometriosis?