['To determine whether paraoxonases (PONs) are expressed in macrophages and to analyze the oxidative stress effect on their expression and activities.', 'We demonstrated the presence (mRNA, protein, activity) of PON2 and PON3 but not PON1 in murine macrophages, whereas in human macrophages, only PON2 was expressed. Under oxidative stress as present in mouse peritoneal macrophages (MPMs) from apoE-deficient (E0) mice as well as in C57BL6 mice, MPMs that were incubated with buthionine sulfoximine, with angiotensin II, with 7-ketocholesterol, or with oxidized phosphatidylcholine, PON2 mRNA levels and lactonase activity toward dihydrocoumarin significantly increased (by 50% to 130%). In contrast, PON3 lactonase activity toward lovastatin was markedly reduced (by 29% to 57%) compared with control cells. The supplementation of E0 mice with dietary antioxidants (vitamin E, pomegranate juice) significantly increased macrophage PON3 activity (by 23% to 40%), suggesting that oxidative stress was the cause for the reduced macrophage PON3 activity. Incubation of purified PON2 or PON3 with E0 mice MPMs resulted in reduced cellular lipid peroxides content by 14% to 19% and inhibition of cell-mediated LDL oxidation by 32% to 39%.'] Is mouse macrophage paraoxonase 2 activity increased whereas cellular paraoxonase 3 activity is decreased under oxidative stress?