AIM: The present study aimed to establish inhibin A and B serum levels during the menstrual cycle of obese women, and its usefulness as an index of luteal-phase follicular development. MATERIALS AND METHODS: Twenty-one obese patients (mean body mass index: 34.9+/-3.7 kg/m2; range: 30.0-45.0 kg/m2) were submitted to basal hormonal measurements and an oral glucose tolerance test after challenge with 75 g glucose. Progesterone and inhibin A and B levels were determined 5-7 days after the menstrual cycle and 7 days prior to expected menses. RESULTS: As expected, an increase in inhibin A and a decrease in inhibin B were observed when first-phase samples were compared with samples obtained after 15-20 days. On the other hand, the percentage variation of both inhibin A and B was at least four times smaller than the values for normal women described previously by other authors employing the same enzyme-linked immunosorbent assays. A small number of obese women presented ovulatory cycles characterized by progesterone concentration higher than 5.8 ng/ml. The percentage elevation (>190%) of inhibin A in the second samples was in agreement with the progesterone levels, but it seemed to be more sensitive for the detection of follicle luteinization. CONCLUSION: We conclude that obese women present less percentage variation of both inhibin A and B during the menstrual cycle, associated with a low frequency of ovulatory cycles. In obese women, the percentage increase of inhibin A can represent an additional marker to recognize follicle luteinization.