Antibiotics of the vancomycin group are shown to enhance their affinities for the bacterial cell wall by the devices of either dimerization (vancomycin and other glycopeptides which dimerize even more strongly) or use of a membrane anchor (teicoplanin); a chelate mechanism is suggested in both cases, as supported by antagonism experiments with the cell wall analog di-N-acetyl-L-Lys-D-Ala-D-Ala. These results may have implications for other binding processes which occur near membrane surfaces.