The need to obtain human monoclonal antibodies has not been overshadowed by the immense success of mouse monoclonal antibody technology. Human monoclonal antibodies will be less antigenic for human in vivo studies and therapy; they will be more likely to recognize antigenic subtleties not easily detected by xenogeneic antibodies, and they will have less rapid catabolism in vivo. The study of human B-cell differentiation and development will be furthered by the availability of human hybridomas. These hybridomas also will be useful to dissect the human humoral immune response in autoimmune disease, cancer, and allergy.