Ovarian cancer arises mostly from the ovarian surface epithelium. The aim of our study was to compare the effects of cytokines in ovarian surface epithelial (OSE) cells and in ovarian carcinoma cells. Proliferation and expression of surface antigens (CA-I25 and classes I and II antigens of the major histocompatibility complex [MHC]) were measured in OSE cells obtained from 7 different patients and 7 ovarian carcinoma cell lines. Proliferation of OSE cells remained unaffected by interferon (IFN)-a or IFN-y, whereas interleukin-I (IL-I) and tumor necrosis factor (TNF) increased cell growth. Proliferation of ovarian carcinoma cells was reduced by both types of IFN as well as TNF but was not affected by IL-I. Expression of the tumor marker CA-125 was increased by IFN-y in ovarian carcinoma cells but not by any other treatment. None of the cytokines affected CA-I25 surface expression in OSE cells. Expression of MHC-I was augmented in OSE and in carcinoma cells by both IFNs but not by the other cytokines. Both types of cell were negative for MHC-II, but IFN-y induced its expression in both OSE and carcinoma cells. Significant concentrations of the cytokines evaluated here have been measured in blood and follicular fluid by several authors. The different actions of these cytokines in OSE and carcinoma cells could therefore be important in understanding the role of such molecules in the regulation of physiological and pathological processes in the ovary, such as ovulation or malignant proliferation.