The phosphate ester base stocks NC-220, NCP and DBPP were administered in the diet to separate groups of 5 male and female Charles River CD rats (Charles River) at a dosage of 5 mg/kg body weight/day for 90 days. A group of 5 male and female rats was administered untreated diet and served as concurrent controls. Animals were observed twice daily for mortality and toxic signs. Once each week, physical examinations were performed and body weights and food consumption were recorded. Blood was collected from all animals at the end of the study and analyzed for variations in hematological values (hematocrit, hemoglobin and erythrocyte, leucocyte, platelet and reticulocyte counts). Plasma and erythrocyte, cholinesterases were also determined at the end of the study.