The mechanism of sensitivity and resistance of various ovarian carcinoma lines to recombinant tumor necrosis factor (rTNF)-mediated cytotoxicity has been investigated using a 24-h 51Cr-release assay. The cell line PA-1 is sensitive to TNF in a dose-dependent manner, whereas the cell line SKOV-3 is resistant to TNF even at high concentrations. The simultaneous addition of TNF and cycloheximide (CHX) in the assay converted the resistant SKOV-3 line into a sensitive line, but no detectable change was observed with PA-1. rTNF inhibited DNA, RNA, and protein synthesis of the sensitive PA-1 line, whereas it had no effect on SKOV-3. This finding was not due to differences in the expression of TNF receptors, as both cell lines expressed equivalent numbers of receptors. The addition of CHX to TNF resulted in suppression of DNA, RNA, and protein synthesis in both the sensitive and the resistant cell lines. Pretreatment of the cell line with TNF for 3 h and subsequent washing resulted in significant cytotoxicity of the sensitive PA-1 line and some cytotoxicity against SKOV-3. However, if the cells were pretreated with CHX for 3 h followed by rTNF for 24 h, a significant decrease in cytotoxicity was observed in both cell lines. Under these conditions, there was no significant inhibition of DNA, RNA, or protein synthesis. Pretreatment of cells for 24 h with TNF and 24 h with CHX resulted in augmentation of the cytotoxicity of PA-1 and SKOV-3, whereas pretreatment for 24 h with CHX followed by 24 h with TNF resulted in no cytotoxicity. Cells pretreated with CHX for 24 h showed poor binding of [125]I-TNF and poor internalization, whereas cells pretreated for 24 h with TNF showed marked enhancement of internalization. The sensitivity of freshly derived ovarian carcinoma lines to TNF and CHX demonstrated that TNF-resistant cells became more sensitive if treated with CHX. These results demonstrate the potential use of metabolic inhibitors in increasing the sensitivity of fresh ovarian tumor cells to TNF.