We used monoclonal antibody, generated against N-acetylglucosaminyl-β1-4-N-acetylmuramyl-alanyl-d-isoglutamine (GMDP), and phage display libraries of random peptides to select for oligopeptides, that mimic GMDP in their biological activity. Selected phage clones displayed a peptide RVPPRYHAKISPMVN (called RN-peptide) on their surface. This peptide was synthesized. RN-peptide was shown to augment the antibody response to ovalbumin in mice while the peptide was non-immunogenic and non-pyrogenic. We also characterized adjuvant activity of 14-, 10- and 7-mer analogs of RN-peptide truncated at the C-terminus and found them to be active. Because both carbohydrate and peptide fragments are critical for the biological activity of muramyl peptides, the results indicate that RN-peptide mimicks the spatial structure of intact GMDP. © 2006 Elsevier Ltd. All rights reserved.