OBJECTIVE To investigate the possibility of local interleukin-1 (IL-1) and IL-1 inhibitor production by human granulosa and cumulus cells and to assess their direct effects on the steroidogenesis of these cells in vitro. METHODS Prospective study. METHODS Normal ovulatory women undergoing ovulation induction for in vitro fertilization. METHODS Pretreatment of patients with gonadotropin-releasing hormone analogue, human menopausal gonadotropin, and human chorionic gonadotropin (hCG). METHODS Retrieval and isolation of granulosa luteal cells and follicular fluid (FF). Granulosa luteal cells and cumulus cells cultured and analyzed by fluorescent activated cell sorter. Follicular fluid separated and bioassayed for IL-1 and IL-1 inhibitory activity. Steroid measurement performed. Interleukin-1 inhibitor purified. Interleukin-1 and IL-1 inhibitor bioassay performed. Statistical analysis made and interpreted. RESULTS Interleukin-1, but not IL-1 specific inhibitory activity, was found in granulosa and cumulus cell cultures and also in FF, only after its purification on a high-pressure liquid chromatography column. Under nonstimulated conditions, neither IL-1 nor IL-1 inhibitor had any effect on basal progesterone (P) or estradiol (E2) secretion. However, IL-1 inhibitor demonstrated significant (P < 0.01) inhibition of hCG-stimulated P secretion (from 200 to 110 ng/10,000 cells per 24 hours). In addition, IL-1 demonstrated a significant (P < 0.05) and dose-dependent inhibition of hCG-stimulated E2 production (from 6,832 +/- 460 to 4,237 +/- 141 pg/10,000 cells per 24 hours). CONCLUSIONS Interleukin-1 may exert a significant local autocrine regulatory role in the human ovary.