Hybridoma technology has revolutionized the diagnosis of human disease. Owing to the unique specificity of monoclonal antibodies (MABs) of murine origin, hundreds of highly sensitive, accurate in vitro diagnostic tests have been developed for clinical laboratory and at-home use. Major research efforts are now underway to exploit this specificity for direct therapeutic purposes: MABs are being used by themselves in treating lymphomas, and in conjugated form with radionuclides, toxins, and chemotherapeutic drugs to treat a variety of tumors. Human MABs now are being tested in tumor imaging and for treatment of infectious diseases. New technologies have been developed to alter the genetic structure of MABs (eg, chimeric antibodies) to increase their treatment efficacy. As development of therapeutic uses for these reagents continues and, especially, as they receive approval for general clinical use, hundreds of kilograms per year will have to be produced. This paper reviews some of the recent developments in this area and describes two novel technologies that have been developed for large-scale cultivation of hybridoma cells.