Cytotoxicity of benzethonium chloride on cultured mammalian cells was studied. Growth of V79 cells, derived from Chinese hamster lung was inhibited by treatment with benzethonium chloride at above 30 micrograms/ml for 24 to 48 hr. Inhibitory effect on survival of V79 cells was not observed in cultures treated with benzethonium chloride at 3 micrograms/ml for 2 to 24 hr. Meanwhile, treatment with benzethonium chloride at 10 micrograms/ml for 2 to 24 hr elicited 11.4% to 75.0% inhibition of cell survival. Exposure of cells to benzethonium chloride at 3 to 30 micrograms/ml for 2 hr resulted in inhibition of DNA-, RNA-, and protein-syntheses of the cells, in a dose-dependent manner.