Monocrotophos (MCP) is a commonly used organophosphorus (OP) pesticide. We studied apoptotic changes in PC12 cells exposed to MCP. A significant induction in reactive oxygen species (ROS), lipid peroxide (LPO), and the ratio of glutathione disulfide (GSSG)/reduced glutathione (GSH) was observed in cells exposed to selected doses of MCP. Following the exposure of PC12 cells to MCP, the levels of protein and mRNA expressions of Caspase-3, Caspase-9, Bax, p53, P(21), Puma, and cytochrome-c were significantly upregulated, whereas the levels of Bcl(2), Bcl(w), and Mcl1 were downregulated. TUNEL assay, DNA laddering, and micronuclei induction show that long-term exposure of PC12 cells to MCP at higher concentration (10(-5) M) decreases the number of apoptotic events due to an increase in the number of necrotic cells. MCP-induced translocation of Bax and cytochrome-c proteins between the cytoplasm and mitochondria confirmed the role of p53 and Puma in mitochondrial membrane permeability. Mitochondria mediated apoptosis induction was confirmed by the increased activity of caspase cascade. We believe that this is the first report showing MCP-induced apoptosis in PC12 cells, which is mitochondria mediated and regulated through the caspase cascade. Our data demonstrates that MCP induced the apoptotic cell death in neuronal cells and identifies the possible cellular and molecular mechanisms of organophosphate pesticide-induced apoptosis in neuronal cells.