We developed a strategy to improve the properties of ligands selected from phagedisplayed random peptide libraries. A sitedirected mutagenesis protocol that introduces mutations and extends the size of a target sequence has been set up to generate diversity in a single or in a population of clones. The pool of mutants thus created is screened to identify variants with the desired properties. We refer to this strategy as in vitro evolution of ligands. Here we report the application of this in vitro evolution protocol to the identification of improved ligands for HCVspecific serum antibodies. A single clone or population of clones were processed to generate a secondary library. Screening of these libraries with sera from HCVinfected patients identified peptides with an enhanced and broadened ability to detect HCVspecific serum antibodies.