Biopanning of a phage library using a Western blotting membrane is difficult because of high background binding. We propose a reliable biopanning method, namely, immunogel-biopanning, which is performed using immunoplates coated with a molecular species fractionated from a crude sample by native polyacrylamide gel electrophoresis (PAGE). The efficacy of this method was determined in model experiments using a human interleukin-18 (IL-18)-specific single chain Fv (scFv) phage clone.