['There is accumulating data that acute coronary syndromes relate to recent onset activation of inflammation affecting atherosclerotic plaques. Increased blood levels of oxidized low density lipoprotein (ox-LDL) could play a role in these circumstances.', 'Ox-LDL levels were measured in 135 patients with acute myocardial infarction (AMI; n=45), unstable angina pectoris (UAP; n=45), and stable angina pectoris (SAP; n=45) and in 46 control subjects using a sandwich ELISA method. In addition, 33 atherectomy specimens obtained from a different cohort of patients with SAP (n=10) and UAP (n=23) were studied immunohistochemically for ox-LDL. In AMI patients, ox-LDL levels were significantly higher than in patients with UAP (P<0.0005) or SAP (P<0.0001) or in controls (P<0.0001) (AMI, 1.95+/-1.42 ng/5 microgram LDL protein; UAP, 1.19+/-0.74 ng/5 microgram LDL protein; SAP, 0.89+/-0.48 ng/5 microgram LDL protein; control, 0.58+/-0.23 ng/5 microgram LDL protein). Serum levels of total, HDL, and LDL cholesterol did not differ among these patient groups. In the atherectomy specimens, the surface area containing ox-LDL-positive macrophages was significantly higher in patients with UAP than in those with SAP (P<0.0001).'] Do elevated levels of oxidized low density lipoprotein show a positive relationship with the severity of acute coronary syndromes?