Ziram as a dithiocarbamate fungicide is widely used throughout the world in agriculture. We previously found that ziram significantly inhibited cytotoxic T lymphocyte activity in a dose-dependent manner. To explore the mechanism of this inhibition, we investigated ziram-induced apoptosis in human T lymphocytes. Jurkat T cells were treated with ziram at 0.031-1 μM for 2-24 h. Freshly isolated primary human T cells were treated with ziram at 0.0625-1 μM for 15 and 24 h. Apoptosis was determined by FITC-Annexin V/PI staining and the TUNEL assay. To explore the mechanism of apoptosis, intracellular levels of active caspases 3, 3/7, 8, and 9 and pan-caspase and mitochondrial cytochrome-c release were determined by flow cytometry. Disruption to mitochondrial transmembrane potential was determined with a MitoLight(™) Apoptosis Detection Kit. We found that ziram induced apoptosis in a time- and dose-dependent manner in both Jurkat cells and primary human T cells. The primary human T cells were more sensitive to ziram than the Jurkat cell line. Ziram induced increases in active caspases 3, 3/7, 8, and 9 and pan-caspase in a dose-dependent manner, and a caspase-3 inhibitor, Z-DEVD-FMK, partially but significantly inhibited the apoptosis. Moreover, a general caspase inhibitor, Z-VAD-FMK, significantly and almost completely blocked the apoptosis. Ziram also disrupted mitochondrial transmembrane potential and caused mitochondrial cytochrome-c release. These findings indicate that ziram can induce apoptosis in human T cells, and the apoptosis is mediated by both the caspase-cascade and the mitochondria/cytochrome-c pathways.