Many fundamental advances in our understanding of the structure and function of eukaryotic genes were derived from the study of antibody genes. Examples include mRNA splicing and rearrangement to generate antibody diversity. The capacity to immortalize an individual B cell using cell fusion permitted the generation of monoclonal antibodies. Monoclonal antibodies have had wide application in many fields of the life sciences and beyond. Recent advances permitting manipulation of antibody genes using recombinant DNA techniques offer many advantages over conventional somatic cell hybridization techniques. Rodent monoclonals can be "humanized" and antibody isotype readily changed. Grafting of the complementarity determining regions from rodent to human framework regions demonstrated the importance of these hypervariable portions of the immunoglobulin to the integrity of the antibody combining site. Recombinant monoclonal antibodies (rMAb) or fragments thereof have been successfully produced in both prokaryotic and eukaryotic hosts at levels equal to those produced by hybridomas. Successful efforts to express rMAbs in plants and other large capacity systems suggest that rMAbs can be produced inexpensively. Use of antibody catalysis and antibodies mimicking various receptors or ligands have numerous applications. Technology developed to immortalize the heavy and light chain repertoire permits the generation in vitro of recombinatorial libraries of antibodies. The capacity to artificially generate high-affinity antibodies in vitro using the methods of recombinant DNA technology has enormous pharmaceutical and industrial potential.