en Clinical Biochemistry Clinical Biochemistry Original Research Original Research Human serum paraoxonase (PON) associated with high density lipoprotein (HDL) , has been postulated to have a role in protecting low-density lipoprotein (LDL) against oxidative damage, which has led to the proposal that PON is an anti-atherogenic and anti-inflammatory enzyme. It has genetic polymorphism at the 191 (R ->Q) and two alloenzymes A and B and three phenotypes A, B, and AB. We examined the activity of arylesterase and paraoxonase among healthy individuals and in patients with hypercholesterolemia. Equal activity distribution was observed among males and females for both enzymes. Arylesterase activity displayed a normal distribution in the population under study. However, paraoxonase activity demonstrated a three modal activity. Population distribution of A, B and AB polymorphism were 46, 10 and 44 percent respectively. A significant direct correlation between paraoxonase activity and triglyceride levels was observed (p<O.05) whereas arylesterase activity was similar among hyperlipidemic and control groups. The lack of a significant relationship between lipids and lipoproteins and PON phenotypes, suggests that PON phenotypes do not influence the lipid profile. Paraoxonase, Arylesterase, Lipids, Lipoproteins, Arteriosclerosis, Polymorphism. 67 73 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-298-181&slc_lang=en&sid=1 A A. SAMADI asamadi@kcom.edu 20031947532846003905 20031947532846003905 Yes From the Dept of Biochemistry, Pasteur Institute of Iran, Tehran S ALVANI 20031947532846003906 20031947532846003906 No the Dept. of Biochemistry, Kashan Medical University, Kashan, Iran M GHAZI-KHONSARI 20031947532846003907 20031947532846003907 No the Dept. of Toxicology, Tehran University of Medical Sciences, Tehran, Iran.