Chinese hamster ovary cells were exposed to 29 toxic chemical substances which were representative of several classes of compounds listed by the Natural Resources Defense Council Consent Decree as priority toxic pollutants. After cell cultures were exposed to the test substance, cell samples were assayed for protein and DNA synthesis, ATP, cell number, and viability. A filter-disk technique employing a batch-washing procedure was used for the determination of protein and DNA synthesis. Dose-response data were obtained for 15 of the more toxic agents including chlorinated aromatics, metallic compounds phenols, and polychlorinated biphenyls. Estimates of the sample concentrations necessary to produce a 50% reduction in response were used to compare cytotoxicity endpoints. ATP and protein synthesis were approximately equally effective as indicators of cellular toxicity. Cadmium chloride, nickel nitrate, arsenic trioxide, and potassium chromate produced a more pronounced effect on DNA synthesis was a smooth, continuous function for responses as low as 1 to 2% of the control.