Specific binding and degradation of native and γ-rays irradiated (100–2000 rad; 100 rad/min; 137C s) human low density lipoprotein by Chinese hamster V79 cells and mouse peritoneal macrophage line, J774G were studied. Low density lipoproteins were labeled with 125I for studying the specific binding and subsequent degradation. The specific binding and degradation of irradiated 125I-low density lipoproteins (mixed with irradiated native lipoprotein) by Chinese hamster V79 cells are considerably reduced. The uptake depends on the concentration of thiobarbutaric acid-reactive products generated in the irradiated lipoproteins which in turn depends on the concentration of carotenoids. In contrast the rate of uptake of oxidized low density lipoproteins is enhanced by Chinese hamster macrophages. The alteration in the surface amino groups of apo-B of low density lipoprotein either due to direct damage of peptide bonds by γ-rays or via interaction with lipid peroxides (generated in the core upon irradiation) are invoked as possible mechanisms for the reduction in specific binding and subsequent degradation by V79 cells.