The cytostatic and cytotoxic effects of recombinant human tumor necrosis factor alpha (rHuTNF alpha) on a cultured nasopharyngeal carcinoma (NPC) cell line were studied. rHuTNF alpha inhibited tritiated thymidine ([3H]TdR) and [14C]leucine incorporation by NPC cells. rHuTNF alpha also inhibited the growth of NPC cells as determined by microphotometry. Cytotoxic effect of rHuTNF alpha was observed 2 days after incubation. Pulse hyperthermia or continuous hyperthermia in combination with rHuTNF alpha treatment was markedly cytotoxic for NPC cells in vitro. Addition of actinomycin D, cycloheximide, puromycin or vincristine sulfate to NPC cells also potentiated the cytotoxic effect of rHuTNF alpha.