We screened a bacteriophage display library of random decapeptides to identify peptide inhibitors of cholesteryl ester transfer protein (CETP). After affinity selection against CETP, bacteriophage-infectedEscherichia coli were plated at clonal density and 36 random clones were isolated. Analysis of the relevant portion of the bacteriophage DNA from a group of 12 clones that had a relatively high affinity for CETP revealed that the corresponding amino acid sequences of the displayed peptides exhibited an ... Xaa-Arg-Met-Arg-Tyr-Xaa ... composite motif. Based on those results, decapeptides from this group were synthesized and one of them, DP1 (NH2-VTWRMWYVPA-COOH), inhibited CETP-catalyzed transfer of cholesteryl esters and triglycerides. Amino- and carboxy-terminal truncations of DP1 demonstrated that the original decapeptide could be reduced to a pentapeptide without loss of either its ability to bind to CETP or its ability to inhibit CETP-mediated lipid transfer. That pentapeptide, NH2-WRMWY-COOH (WRMWY, PNU-107368E), binds directly to CETP and its inhibition is consistent with that of a competitive inhibitor of CETP with aKi of 164 µM. WRMWY or modified versions of this peptide may be useful in studying the interactions between CETP and plasma lipoproteins.