The present study was to test the relative hypercholesterolaemic and atherogenic potency of oxidised cholesterol (OxC) and non-oxidised cholesterol in hamsters. An OxC mixture, prepared by heating pure cholesterol (100 g) at 160 degrees C in air for 72 h, contained 78 % cholesterol and 22 % OxC. Fifty Golden Syrian hamsters were randomly divided into five groups of ten animals and fed the control diet, a 0.05 % cholesterol diet (C-0.05), a 0.10 % cholesterol diet (C-0.1), a 0.05 % OxC mixture diet (OxC-0.05) or a 0.10 % OxC mixture diet (OxC-0.1), respectively. The OxC-0.05 and OxC-0.1 groups were more hypercholesterolaemic and had serum total cholesterol 22 and 12 % higher than the corresponding C-0.05 and C-0.1 hamsters (P < 0.05). The OxC-0.1 group demonstrated greater deposition of cholesterol and had a larger area of atherosclerotic plaque in the aorta than the corresponding C-0.1 hamsters (P < 0.05). Similarly, the aorta in the OxC-0.1 group showed greater inhibition on acetylcholine-induced relaxation compared with that in the C-0.1 hamsters. It was concluded that OxC was much more hypercholesterolaemic and atherogenic than cholesterol.