Apoptosis is a term used to describe certain forms of physiological cell death that occur during embryogenesis, differentiation, and normal cell turnover. Previous reports concerning the effects of calcium ionophores on rodent thymocytes and the pore-forming proteins perforin and staphylococcal alpha-toxin on murine tumor cells led to the suggestion that simply raising intracellular calcium causes apoptotic cell death. This hypothesis was tested using two ionophores, A23187 and valinomycin, and two pore-forming agents, melittin and staphylococcal alpha-toxin, on four murine tumor cell lines. Although treatment with these agents could raise intracellular calcium, and in some instances cause DNA fragmentation, only valinomycin caused apoptosis. In contrast to previous reports, our results suggest that raising intracellular calcium and inducing internucleosomal DNA fragmentation is not sufficient to elicit apoptotic cell death in all cell types.