Up to 5% of cholesterol esters were hydrolyzed after incubation of blood serum low density lipoproteins (LDL) with pancreatic cholesterol esterase free of proteinases and phospholipase activity in absence of detergents. The surface layer of the lipoprotein particles appears to contain about 5% of cholesterol esters. More active intracellular accumulation of cholesterol esters was found in fibroblasts cultivated in a medium containing modified LDL as compared with cultivation in presence of native LDL. Deterioration of normal interrelations between free cholesterol and its esters appears to be responsible for alterations in the LDL structure and contributed to more active transport of cholesterol into cells.