In this narrative, I describe how my interest in the nature and origin of antibody diversity led me to tackle the problem by using somatic cell genetic techniques. The first hybridoma (an immortal antibody-secreting cell line derived by fusion of a short-lived lymphocyte and a myeloma cell line) was an offshoot of this approach. Although not intended for such purposes, it soon became obvious that this invention had widespread potential in basic research and industry. Indeed, the technique opened new inroads into the study of complex biological substances and became the method of choice to define new differentiation markers. Hybridomas also allowed us to dissect the immune response to a simple antigen and to demonstrate the critical role of somatic mutations in the generation of high affinity antibodies. Now, monoclonal antibodies can be derived and manipulated in vitro, leading to important new developments in therapeutic applications. BioEssays 1999;21:966–973. © 1999 John Wiley & Sons, Inc.