High concentrations of zinc salts (500 microM and greater) are known to inhibit apoptosis in a variety of systems. However, closer examination of dose effects revealed that lower concentrations of zinc (80-200 microM) could induce apoptosis in approximately 30-40% of mouse thymocytes following 8 h incubation. The ability of zinc to cause thymocyte apoptosis was detected flow-cytometrically by reduction in propidium iodide DNA fluorescence and forward scatter, both quantitative indicators of apoptotic death. Zinc induced both internucleosomal DNA fragmentation and morphological changes characteristic of apoptosis as determined by gel electrophoresis and electron microscopy, respectively. In addition, transcriptional and translational inhibitors prevented zinc-induced apoptosis, indicating a requirement for de novo mRNA and protein synthesis, another characteristic of apoptotic death. Fluorescent immunophenotype-specific apoptotic analysis indicated that zinc-induced apoptosis occurred primarily in the less mature CD4+CD8+ alpha beta TCRloCD3 epsilon lo thymocyte subset, with lower amounts of death occurring in the other subsets. This lineage specificity was shared with glucocorticoid-induced apoptosis. Taken together, these results indicate that zinc induces true apopotitic death in mouse thymocytes and suggests a role for zinc in the regulation of apoptosis.