Interferons have a mechanism of action different from chemotherapeutic agents. They modulate many physiologically important cellular functions and are a major building block in the network constructed by the biological response modifiers. Moreover, interferons are known to interact also with anticancer drugs to increase their therapeutic benefit. The aim of the present study was to evaluate the effects of interferon-gamma on cultured ovarian carcinoma cell lines. The growth of 3 out of 4 carcinoma cell lines (OVCAR-3, HTB-77, 2780 vs CRL-1572) was inhibited by interferon-gamma. The same cell lines which were growth inhibited also showed an induction of HLA-DR on their surface. CA-125 was found to be increased in 2 of them (OVCAR-3 and HTB-77) by interferon-gamma, whereas CEA was not detectable even after treatment. For HMFG-I, a shightly increased surface expression was induced on OVCAR-3 cells. HMFG-II expression was not significantly affected by interferon-gamma. The combined treatment with interferon-gamma and cisplatin, retinoic acid, or tumor necrosis factor alpha was studied on the ovarian carcinoma cells. For the combination with cisplatin we observed an additive or synergistic amplification of the antiproliferative activity, whereas tumor necrosis factor alpha resulted in a marked synergism in each case. In contrast to breast cancer cells retinoic acid and interferon-gamma acted synergistically only in one ovarian carcinoma cell line.