The influence of partial hepatectomy on the level of 2-aminofluorene (2-AF) induced DNA adducts in rat liver was studied. We found that partial hepatectomy performed either 3 weeks before or simultaneously with the injection of 2-AF affected the amounts of adducts in rat hepatic DNA compared to controls. The level of DNA adducts in rats that were treated with 2-AF and simultaneously hepatectomized was higher (19.9 fmol/microgram DNA) than in non-hepatectomized ones (14.4 fmol/microgram DNA) when measured 48 h after 2-AF administration. In rats treated with the carcinogen 3 weeks after hepatectomy the level of DNA adducts was significantly higher than in nonhepatectomized rats when measured 15 days after the injection of 2-AF (10.9 fmol/microgram DNA and 5.9 fmol/microgram DNA respectively). The high level of DNA adducts in that group of hepatectomized animals was correlated with a relatively lower rate of 2-AF-induced radioactive thymidine incorporation into hepatic DNA (in comparison to non-hepatectomized rats).