Abstract Cremophor EL, a surfactant for pharmaceutical products, augments the cytotoxicity of hydrogen peroxide in rat thymocytes [Iwase, K., Oyama, Y., Tatsuishi, T., Yamaguchi1, J., Nishimura1, Y., Kanada, A., Kobayashi, M., Maemura, Y., Ishida, S., Okano, Y., 2004. Cremophor EL augments the cytotoxicity of hydrogen peroxide in lymphocytes dissociated from rat thymus glands. Toxicol. Lett. 154, 143–148]. The effect of cremophor EL on Ca 2+-dependent process of cell death has been examined using a flow cytometer since hydrogen peroxide increases intracellular Ca 2+ concentration. Cremophor EL at clinically-relevant concentrations greatly increased the population of dead cells in rat thymocytes simultaneously treated with A23187, a calcium ionophore increasing intracellular Ca 2+ concentration. Removal of Ca 2+ from external solution diminished the cremophor EL-induced increase in the dead cell population. Result suggests that Ca 2+-dependent process is involved in the cremophor EL-induced decrease in the cell viability in the simultaneous presence of A23187. The population of cells with hypodiploidal DNA was not increased by the application of cremophor EL and A23187 although the cell viability was greatly decreased, indicating that the type of cell death is necrosis. It is suggested that cremophor EL at clinically-relevant concentrations augments the Ca 2+-dependent process of necrosis.