The biotechnological generation of high affinity monoclonal antibodies (MAbs) has traditionally involved the production of hybridomas from spleen cells of immunized animals (1 ). This event, together with availability of increasingly sophisticated molecular biology and protein engineering techniques, opened up the field of numerous applications and benefits in not only the medical but also industrial world. Now the use of phage antibodies offers a new route for the generation of antibodies, including antibodies of human origin, which cannot be easily obtained by conventional hybridoma technology. Recent advances in the expression of antibody fragments in E. coli (2 ,3 ) and the application of the polymerase chain reaction (4 ) for cloning of immunoglobulin DNA (5 ,6 ) have mainly contributed to these achievements. With phage display, antibodies can be made completely in vitro, bypassing the immune system and the immunization procedures.