This study examines the possible direct effect of interleukin-1 alpha (IL-1 alpha) upon human granulosa cells. The cells were isolated from follicles of stimulated cycles in women undergoing oocyte retrieval for in-vitro fertilization. Purified cell preparations were cultured for different time periods in the presence of IL-1 alpha and human luteinizing hormone (LH) or follicle stimulating hormone. IL-1 alpha stimulated basal as well as LH-induced progesterone accumulation. The response in terms of cyclic AMP was more complex, there was no effect of IL-1 alpha on basal cyclic AMP accumulation. However, at the highest concentration tested (50 IU/ml), IL-1 alpha enhanced cyclic AMP accumulation over that seen with LH alone. At a lower concentration, IL-1 alpha either had no effect or was slightly inhibitory to the LH-induced cyclic AMP accumulation, depending on the culture period. Our results, taken together with other findings, are compatible with the view that IL-1 alpha has a potential regulatory role in the granulosa-luteal cell transition in the human ovary.