The development of monoclonal antibodies to human tumor associated antigens has greatly facilitated the application of immunohistochemical techniques to analyze surgically removed tissues. During the last few years this approach has been utilized by a progressively increasing number of investigators to analyze malignant cells. Although monoclonal antibodies to tumor associated antigens have not become yet routine reagents in immunopathology, they have provided new information which could not be obtained with conventional antisera or histochemical procedures. The following are representative...