Mercuric chloride (HgCl2) as well as several drugs can induce T cell activation leading to systemic immune-mediated diseases in genetically susceptible individuals or rodents. T cell hybridomas represent a well-characterized model system for in vivo mechanisms of various stimuli-induced cell death. The cellular response to HgCl2 was examined using various T cell lines and particularly the murine T cell hybridoma 2B4.11. Exposure to HgCl2 induced both necrosis and apoptosis in a dose- and time-dependent way as demonstrated by DNA fragmentation analysis, flow cytometry of the whole cells and of isolated nuclei, and morphological examination. HgCl2-induced cell death was partly inhibited by cycloheximide. The expression of human Bcl-2 in 2B4.11 cells after transfection significantly prevented HgCl2-induced cell death but did not affect the susceptibility to apoptosis induced by an anti-CD3 epsilon mAb. Subcytotoxic doses of HgCl2 enhanced metabolic activity of Bcl-2 transfectants in contrast with mock-transfected cell line. Thus, we conclude that apoptosis is part of the cell death process induced by HgCl2 and that the ability of Bcl-2 to prevent the death of one particular cell line is stimulus-dependent suggesting the existence of different pathways leading to cell death.