Methyl bromide is widely used as an insecticidal fumigant in food supplies, warehouses, barges, buildings, and furniture. Its popularity as a fumigant is largely attributable to its high toxicity to many pests, the variety of settings in which it can be applied, its ability to penetrate the fumigated substances, and its rapid dissipation following application. Because of its frequent use around humans and human-related activities and its high acute toxicity, methyl bromide-related fatal accidents have occurred. The primary route for human exposure to methyl bromide is inhalation. In California, the most frequent cause of death from methyl bromide exposure in recent years has been unauthorized entry into structures under fumigation. The most frequently reported lesions included pulmonary edema, congestion, and hemorrhage. In recent years, a great deal of effort has been given to the characterization of the toxicity of methyl bromide because of its commercial value and its direct and indirect economic importance. Methyl bromide is acutely very toxic. Subchronically and chronically, the principal target site for methyl bromide appears to be the central nervous system. However, there was no evidence for carcinogenic activity of methyl bromide following the normal environmental exposure routes of inhalation or oral intake through residue on foods. Methyl bromide is clearly genotoxic in vitro and in vivo, as evidenced by the positive results from various tests. The mechanism of toxicity for methyl bromide is currently uncertain, although its alkylating property as well as the possibility of forming a reactive intermediate through metabolic transformation remain attractive hypotheses.