4F is an anti-inflammatory, apolipoprotein A-I (apoA-I)-mimetic peptide that is active in vivo at nanomolar concentrations in the presence of a large molar excess of apoA-I. Physiologic concentrations (∼35 μM) of human apoA-I did not inhibit the production of LDL-induced monocyte chemotactic activity by human aortic endothelial cell cultures, but adding nanomolar concentrations of 4F in the presence of ∼35 μM apoA-I significantly reduced this inflammatory response. We analyzed lipid binding by surface plasmon resonance. The anti-inflammatory 4F peptide bound oxidized lipids with much higher affinity than did apoA-I. Initially, we examined the binding of PAPC (1-palmitoyl-2- arachidonoyl-sn-glycero-3-phosphatidylcholine) and observed that its oxidized products bound 4F with an affinity that was ∼4-6 orders of magnitude higher than that of apoA-I. This high binding affinity was confirmed in studies with defined lipids and phospholipids. 3F-2 and 3F14 are also amphipathic α-helical octadecapeptides, but 3F-2 inhibits atherosclerosis in mice and 3F14 does not. Like 4F, 3F-2 also bound oxidized phospholipids with very high affinity, whereas 3F14 resembled apoA-I. The extraordinary ability of 4F to bind pro-inflammatory oxidized lipids probably accounts for its remarkable anti-inflammatory properties. Copyright © 2008 by the American Society for Biochemistry and Molecular Biology, Inc.