It has been reported that interleukin (IL)-1 beta induces the synthesis of both nitric oxide (NO) and prostaglandin (PG)E2 in cultures of dispersed ovarian cells and exerts cytotoxic effects on these cells. Since PGE2, NO and IL-1 beta have been implicated as modulators of steroidogenesis, experiments have been undertaken to determine how IL-1 beta-induced NO and PGE2 production may affect steroidogenesis in cultures of ovarian dispersates obtained from untreated adult oestrous rats and to compare the action of IL-1 beta in cultures of granulosa/luteal (GL) cell-only cultures and GL cells co-cultured with peritoneal macrophages. IL-1 beta significantly increased the production of NO (assessed by nitrite measured in the culture medium) and PGE2 in cultures of ovarian dispersates but had no effect on cultures of GL cells in which NO production was typically very low and PGE2 production was undetectable. In contrast both NO and PGE2 were high in co-cultures and were not significantly altered by the addition of IL-1 beta. The NO donor sodium nitroprusside inhibited steroidogenesis in cultures of ovarian cells in a dose-dependent manner while PGE2 had a stimulatory effect. Concomitant inhibition of NO production with aminoguanidine and PG production with indomethacin resulted in a significant enhancement of basal progesterone production in these cultures. Finally, IL-1 beta inhibited progesterone responses to forskolin and PGE2 in ovarian dispersates: an effect not observed in GL cell-only cultures nor in co-cultures in which forskolin-induced progesterone production is always inhibited. No cytotoxic effects of IL-1 beta during the 48 h period of culture were observed. A comparison of the steroidogenic NO and PGE2 responses to IL-1 beta in the three culture models suggests that (i) the response to IL-1 beta observed in ovarian dispersates could be due to cytokine activation of resident and infiltrating macrophages or that the action of IL-1 beta requires some other heterologous cell-cell contact, and (ii) IL-1 beta acts indirectly on signal transduction pathways which stimulate steroidogenesis.