1,2-Dichloropropane (1,2-DCP) and dichloromethane (DCM) are possible causative agents associated with the development of cholangiocarcinoma in employees working in printing plant in Osaka, Japan. However, few reports have demonstrated an association between these agents and cholangiocarcinoma in rodent carcinogenicity studies. Moreover, the combined effects of these compounds have not been fully elucidated. In the present study, we evaluated the in vivo mutagenicity of 1,2-DCP and DCM, alone or combined, in the livers of gpt delta rats. Six-week-old male F344 gpt delta rats were treated with 1,2-DCP, DCM or 1,2-DCP+DCM by oral administration for 4weeks at the dose (200mgkg(-1) body weight 1,2-DCP and 500mgkg(-1) body weight DCM) used in the carcinogenesis study performed by the National Toxicology Program. In vivo mutagenicity was analyzed by gpt mutation/Spi(-) assays in the livers of rats. In addition, gene and protein expression of CYP2E1 and GSTT1, the major enzymes responsible for the genotoxic effects of 1,2-DCP and DCM, were analyzed by quantitative polymerase chain reaction and western blotting. Gpt and Spi(-) mutation frequencies were not increased by 1,2-DCP and/or DCM in any group. Additionally, there were no significant changes in the gene and protein expression of CYP2E1 and GSTT1 in any group. These results indicated that 1,2-DCP, DCM and 1,2-DCP+DCM had no significant impact on mutagenicity in the livers of gpt delta rats under our experimental conditions. Copyright (c) 2016 John Wiley & Sons, Ltd.