BACKGROUND AND AIM OF THE STUDY: Aortic valve stenosis (AS) is the most common valvular heart disease in the western world, and in adults is invariably caused by the calcification of a normal tricuspid or congenital bicuspid valve. Calcific AS, as an active disease process, is characterized by lipid accumulation, inflammation and calcification that mimic atherosclerosis. Paraoxonase-1 (PON-1) is a high-density lipoprotein (HDL)-bound enzyme that exerts antiatherogenic properties by protecting low-density lipoprotein (LDL)-cholesterol from oxidative modification. The study aim was to examine the association between PON-1 activity and AS. METHODS: A total of 93 patients with angiographically normal coronary arteries was enrolled into the study. Transthoracic echocardiography was used to diagnose and grade the AS before the patients underwent selective coronary angiography. The patients were allocated to three groups of mild AS (n = 34), moderate AS (n = 31) and severe AS (n = 28). Paraoxonase activity was measured using a spectrophotometric technique. RESULTS: The mean PON-1 activity in patients with severe AS (64.4 +/- 29.8 U/l) was significantly lower than that in patients with mild and moderate AS (97.1 +/- 72.6 and 146.8 +/- 133.9 U/l; p = 0.03 and p = 0.002, respectively). Typically, PON-1 activity tended to be lower in moderate AS than in mild AS (p = 0.07). The serum PON-1 activity correlated positively with the aortic valve area, but negatively with the aortic mean and maximum gradients. CONCLUSION: The study results showed that PON-1 activity is lower in patients with calcific AS. In addition, PON-1 activity was inversely correlated with the severity of AS.