Human granulosa cells, obtained either from natural or stimulated cycles, were cultured, and the response to IGF-I and GH was analyzed. It was found that IGF-I alone stimulated thymidine incorporation in both types of granulosa cells. Furthermore, IGF-I alone and in combination with FSH or LH enhanced estradiol and progesterone production. In a limited series of experiments, GH in combination with FSH was found to stimulate steroidogenesis in granulosa cells obtained from natural, but not from stimulated, cycles.