The advent of hybridoma technology leading to the successful produc tion of monoclonal antibodies against a variety of tumor-associated antigens has, during the last decade, provided a very powerful tool for research and clinical investigations. These highly specific reagents have essentially replaced the polysera of the earlier days. The successful demonstration of the many wide ranging capabilities of the monoclonal antibody technique has already begun to exert an enormous impact on diverse areas of research in basic science and medicine. In particular, the potential of monoclonal...