Di-(2-ethylhexyl) adipate (DEHA) was fed to groups of twenty female Fischer 344 strain rats or thirty B6C3F1 strain mice at dietary levels of 0(control), 0.012, 0.12, 1.2 or 2.5% for up to 21 days. In both species there was also a recovery group of ten rats and twenty mice fed 2.5% DEHA for 21 days followed by 14 days on control diet, matched with a second control group fed the basal diet for 35 days. Body weights and food intakes were monitored prior to and throughout the treatment and recovery periods. After 3, 7 or 21 days of treatment five animals of both species from each dietary level were given at intraperitoneal dose of ((sup 3) H-methyl) thymidine and killed one hour later for the collection of liver samples for the assay of DNA concentration and ((sup 3)H) thymidine uptake. At the 21 day examination additional rats and mice were killed and blood collected for the determination of serum triglycerides, total cholesterol, total bilirubin, alanine aminotransferase and alkaline phosphatase. The livers, kidney and spleens were weighed and preserved for histological examination. In addition, samples of liver were processed for electron microscopic examination of peroxisomes and for histochemical demonstration of neutral fat.