Phage display technology is a powerful tool to find ligands with high affinities to given targets.Arguably the most successful use of display technologies has been the isolation of specific antibodies from large antibody libraries displayed on filamentous phage.A number of new, large libraries based on synthetic single-chain-Fv fragment (scFv) were described recently.Specific antibody usually was obtained through scFv phage display technologies, but the accurate number of scFv fragments displayed on the surface of each phage was still unknown, led to the evaluation of phage library properties only based on the volume of phage transformed by external gene fragments.