Interleukin-10, one of the most potent antiinflammatory cytokines, is expressed in ovarian carcinomas in vivo. In contrast to the high levels of IL-10 in ascites and tumour tissue, the expression of this cytokine appears to be a rare event in ovarian carcinoma cell lines in vitro. Virtually nothing is known about the regulation of IL-10 expression in ovarian carcinoma cell lines. We investigated the expression of IL-10 in four cell lines originally derived from ovarian serous adenocarcinoma: OVCAR-3, SKOV-3, CAOV-3 and OAW-42. IL-10- specific mRNA was detected in OVCAR-3 and only this cell line produced IL-10 constitutively under serum-free conditions as well as in serum-containing medium. Our studies on the regulation of IL-10 secretion in OVCAR-3 revealed that (1) proinflammatory stimuli IL-1beta and TNF-alpha, but not LPS, enhance IL-10 secretion, (2) IL-6 has no influence on the release of IL-10, (3) prostaglandin E2 influences neither the spontaneous nor the TNF-alpha- or IL-1beta-stimulated IL-10 production and (4) interferon-gamma inhibits IL-10 secretion. We conclude that only a minority of serous ovarian carcinoma cells maintain the ability to produce IL-10 in vitro. Our data on the regulation of IL-10 production in OVCAR-3 indicate that ovarian carcinoma cells share some, but not all, of the regulatory features typical for the monocytic IL-10 secretion.