Chronic toxicity and oncogenicity of dichloromethane were evaluated in groups of B6C3F1 mice exposed to dichloromethane orally in deionized drinking water at nominal target dose levels of (number of males/females): 0 (60/50), 0 (65/50), 60 (200/100), 125 (100/50), 185 (100/50) or 250 mg/kg/day (125/50) for 24 months. There were no significant differences between treated animals and controls in the following: tissue masses, body weights, water consumption, leukocyte counts, necropsy findings, or histopathology with respect to focal or multifocal hepatocellular hyperplasia, proliferative hepatocellular lesions, adenoma or carcinoma. The only significant sign of toxicity was a marginal increase in the amount of positively staining material in the livers of high-dose groups of both sexes.