This invention relates to novel peptides, discovered by using phage display technique, that bind to VAP-1 (Vascular Adhesion Protein-1). The invention concerns also peptides useful as VAP-1 ligands. Such peptides constitute a portion of natural proteins that are present in the individual. The invention relates particularly to a peptide chain in the leukocyte surface protein, where said peptide chain is useful as a ligand for the VAP-1 molecule and thus facilitates the binding of leukocytes to the vascular endothelium. Furthermore, the invention relates to pharmaceutical and diagnostic compositions for targeting VAP-1 in vivo.