['To examined whether serum paraoxonase (PON1) and arylesterase (ARE) activities are correlated with inflammatory biomarkers (procalcitonin and high sensitivity C-reactive protein (hs-CRP) in patients with acute coronary syndrome (ACS).', 'This cross-sectional study was conducted at the Departments of Cardiology and Biochemistry, Uludag University School of Medicine, Bursa, Turkey, from April 2007 to December 2007. Seventy-eight consecutive patients with ACS and 39 healthy controls were investigated. Acute coronary syndrome patients were divided into 3 groups according to their clinical presentation: unstable angina pectoris (UAP) (Braunwald III-B, n=25), non-ST elevation myocardial infarction (NSTEMI) (n=18), and ST-elevation myocardial infarction (STEMI) (n=35). Serum PON1/ARE activities were measured spectrophotometrically. Levels of procalcitonin and hs-CRP were measured by immunoassay.', 'Paraoxonase/ARE activities were significantly lower in all patient groups compared to controls. No correlation between PON1/ARE activities and high-density-cholesterol levels was seen. Among ACS patients, serum ARE activity correlated inversely with baseline and 48-hour procalcitonin (r=-0.577, p=0.009, and r=-0.642, p=0.019) and hs-CRP levels (r=-0.614, p=0.03, and r=-0.719, p=0.044).'] Is serum arylesterase activity negatively correlated with inflammatory markers in patients with acute coronary syndromes?