provided some of the earliest evidence for an extensive repertoire of immunoglobulin molecules. The implications of these findings have been amply confirmed by recent studies of protein struc­ ture and molecular genetics; many of these studies are reviewed in the present volume. It is known now that the diversity of antibodies is based on the presence of numerous V and L V H genes, on recombinatorial events involving D and] segments, on somatic mutations, and on processes involving deletion of DNA followed by repair with errors, including inser­ tions. Each of these parameters is capable of influencing the idiotype expressed by the final immunoglobulin product. Regulation of the immune response is another area in which idiotypy has significantly influenced modern immunology.