Phage displaying random cyclic 7-mer, and linear 7-mer and 12-mer peptides at the N-terminus of the coat protein, pIII were panned with the murine monoclonal antibody, 9-2-L379 specific for meningococcal lipooligosaccharide. Five cyclic peptides with two sequence motifs, six linear 7-mers and five linear 12-mers with different sequence motifs were identified. Only phage displaying cyclic peptides were specifically captured by and were antigenic for 9-2-L379. Monoclonal antibody 9-2-L379 exhibited ¡§apparent¡¨ binding affinities to the cyclic peptides between 11 ¡V 184nM, comparable to lipooligosaccharide. All cyclic peptides competed with the binding of 9-2-L379 to lipooligosaccharide with EC50 values in the range 10 ¡V 105ƒÝM, which correlated with their ¡§apparent¡¨ binding affinities. Structural modifications of the cyclic peptides eliminated their ability to bind and compete with mAb 9-2-L379. Mice (C3H/HeN) immunised with the cyclic peptide with optimal ¡§apparent¡¨ binding affinity and EC50 of competition elicited cross-reactive antibodies to meningococcal lipooligosaccharide with end-point dilution serum antibody titres of 3200. Cyclic peptides were converted to T-cell dependent immunogens without disrupting these properties by C-terminal biotinylation and complexing with NeutrAvidin„¥. The data indicate that constrained peptides can cross-react with a carbohydrate-specific antibody with greater specificity than linear peptides, and critical to this specificity is their structural conformation.