Two ovarian cancer cell lines, 3AO and NIH: OVCAR-3, were used in this study to assess the synergistic effect of TNF and IFN gamma in combination. The result showed that these two ovarian cancer cell lines were all resistant to TNF and IFN gamma individually, but sensitive to the combined administration of TNF and IFN gamma. Concentration of 1 x 10(4) U/L of TNF and IFN gamma significantly inhibited 3AO and NIH: OVCAR-3 ovarian cancer cells (P < 0.05). Administration of 1 x 10(6) U/L TNF and IFN gamma could inhibit the growth of 3AO cells by 55% and NIH: OVCAR-3 cells by 75% (P < 0.01). It suggests that in some ovarian cancer cells which resistant to TNF could be changed to TNF sensitive cells by IFN gamma. anticancer treatment higher antitumor activity could be achieved by combined administration of TNF and IFN gamma.