The present report shows that the simultaneous application of two biological response modifiers (recombinant human γ-interferon plus recombinant human α-tumor necrosis factor) has a lethal effect on living laryngeal and salivary gland carcinomas. A cytostatic or cytotoxic effect of the two substances alone could only be observed in occasional cases. The results suggest a synergistic action of γ-interferon and α-tumor necrosis factor that might be of therapeutic value for head and neck carcinomas in the fut