We have constructed two phagemid vectors containing the gene coding for human Prostate Specific Antigen (PSA) translationally fused to a pelB signal sequence and minor coat protein III of phage fd leading to phage particles that carry PSA on their tips. Phages were characterized by Western blotting and by panning, using biotinylated monoclonal anti-PSA antibodies immobilized onto streptavidin-coated microtitration wells. Binding of PSA-phages was 10(2)- to 5 x 10(3)-fold more effective than that of wild-type phages. Trypsin treatment of the phage abolished the specific binding. Competitive panning with different concentrations of added purified PSA demonstrated that binding was PSA specific. Finally, Western-blot analysis confirmed that full-length and shorter degradation products of the fusion between PSA and protein III were visible as probed with anti-PSA antibody.