Cholesterol fed to male rats and rabbits for 120 days impaired testicular function. The production of secondary spermatocytes in rats and rabbits was reduced by 26.1% and 46.9%, respectively. There was significant reduction in spermatid cell population, seminiferous tubules, and Leydig's cell nuclear dimensions. In rats aortic endothelium showed some alterations while in rabbits full-blown atherosclerotic plaque containing a necrotic core and a proliferative fibrous cap was found. Total cholesterol, triglycerides and phospholipids of the testes were increased whereas, testicular glycogen was significantly reduced. Three- and sevenfold increases were noticed in the serum cholesterol levels of rats and rabbits. The LDL cholesterol values were increased while the HDL cholesterol/Total cholesterol ratio was significantly decreased (P less than 0.001). It is concluded that hypercholesterolemia affects the testicular function and aortic endothelium.