To test the hypothesis that leptin signals metabolic information to the reproductive system in cattle by directly affecting IGF-I-induced ovarian cell function, granulosa and thecal cells from bovine ovarian follicles were cultured for 2 d in serum-free medium with added hormones. Recombinant human leptin at 30 and 300 ng/mL had no effect on basal thecal cell steroidogenesis or thecal cell numbers. However, 300 but not 30 ng/mL of leptin attenuated (p < 0.05) luteinizing hormone-induced androstenedione production by 24% in the absence of IGF-I and by 16% in the presence of IGF-I. Leptin had no effect on IGF-I-induced estradiol production in the presence of follicle-stimulating hormone (FSH), but at 100 ng/mL, leptin inhibited (p < 0.05) FSH plus IGF-I-induced progesterone production and granulosa cell proliferation by 29 and 31%, respectively. Leptin did not compete for 125I-IGF-I binding to granulosa or thecal cells, whereas unlabeled IGF-I did. In conclusion, leptin has weak inhibitory effects on gonadotropin- and/or IGF-I-induced steroidogenesis of thecal and granulosa cells.