The administration of 30% glucose in drinking water to rats for 48 h caused a significant increase in the hepatic S9-mediated mutagenicity of aflatoxin B1, in Salmonella typhimurium TA100 and in the binding of aflatoxin B1, to calf thymus DNA in vitro. These effects correlated with a reduction in the metabolism and detoxification of aflatoxin B1, by S9 from glucose-treated rats and suggest that the oral intake of sugar may affect the hepatocarcinogenicity of aflatoxin B1. © 1990.