Temozolomide is a triazene that undergoes rapid chemical conversion to the active 3-methyl-(triazen-1-yl)imidazole-4-carboxamide (MTIC) at physiological pH. The cytotoxicity of MTIC is thought to be primarily due to alkylation of guanine at the O6 position and additional alkylation at the N7 position. The resulting cytotoxic effects appear to involve a mechanism of aberrant methyl reduction.