Atherosclerosis is a chronic inflammatory process, and myeloperoxidase (MPO) seems to contribute directly to the pathogenesis of acute coronary syndrome (ACS).To compare MPO levels among the patients with stable and unstable ischemic heart disease and to evaluate their independent prognostic value for cardiovascular events.MPO and C-reactive protein (CRP) were assessed in two cohorts of coronary artery disease patients, including 178 patients with stable angina and 130 patients with ACS evaluated at the emergency department.MPO and CRP levels were significantly higher among patients with ACS [MPO 93 (54-127) vs. 9.9 pmol/l (5-21) and high sensitivity-CRP 11 (3-27) vs. 2.6 mg/l (1-5)]. Among patients with stable angina, high sensitivity-CRP levels greater than 3 mg/l were associated with a three-fold risk of further cardiovascular events during a mean follow-up period of 13+/-4 months, although there was no significant association between MPO levels and outcomes. Among patients with ACS, baseline MPO level was an independent predictor of major adverse cardiac events during hospitalization, odds ratio of 3.8 (95% confidence interval: 1.2-12) for the combined endpoint (death, recurrent angina, heart failure, and arrhythmia). CRP levels were associated with hospital mortality in patients with ACS, but were not independently related to cardiovascular events.Elevated MPO levels among the ACS patients suggest that this marker may participate in plaque vulnerability and instability process, whereas higher CRP levels were predictive of cardiac events only among the stable angina patients. These findings suggest distinct role of the inflammatory markers studied in the pathophysiology of coronary artery disease.