Basic research has provided strong evidence that oxidation of LDL plays an important role in the progression of atherosclerotic vascular disease. The levels of plasma oxidized two-density lipoprotein (ox-LDL) were measured by sandwich ELISA using the monoclonal antibody (DLH3) recognized oxidatively modified lipoproteins and the anti-human apolipoprotein B monoclonal antibody in healthy subjects and patients with coronary heart disease (CHD). Plasma ox-LDL could be detected in normal subjects and patients with CHD. No sex-related difference was observed in normal subjects. The levels of ox-LDL in the forties and fifties were higher than those in the thirties and twenties. The levels of plasma ox-LDL were significantly higher in patients with CHD than in controls. There was no difference between the levels of ox-LDL of patients with single vessel disease and those with multivessel disease. These results suggest that elevated levels of oxidized LDL may be a marker for CHD.