The combination of an optimized arginine receptor unit with a semirigid linker carrying a strategically placed primary ammonium group leads to the first synthetic receptor in xylylene-based tris(phosphonate) I for RGD peptides. I binds to the free RGD peptide as well as to cyclo(RGDfV) in water with assocn. consts. around 1000 M-1. RGD mimetics such as benzamidine deriv. II are not recognized, rendering I as a new class of synthetic receptors selective for the true RGD sequence in peptides.