Although monoclonal antibody technology has only been with us for slightly more than 10 years, it has already had a great impact on both basic science and clinical medicine. The ability to use these antibodies as highly specific and sensitive reagents that are consistent from batch to batch is invaluable. Because of this ability, monoclonal antibodies are assuming an ever more important role in laboratory assays. In addition, immunohistochemical techniques employing monoclonal antibodies enhance the histologic characterization of pathologic specimens. These clinical benefits are real but are often hidden from the eyes of the physician taking care of his patient. However, other newer uses of monoclonal antibodies are much more spectacular. Clinical imaging with monoclonal antibodies has been shown to be feasible in a variety of systems. Antibodies to colon cancer and melanoma have detected metastatic tumors that were otherwise hidden clinically. Despite these triumphs, the routine use of radioimmunodetection employing radiolabeled monoclonal antibodies has not yet arrived. However, the preliminary data obtained so far are very promising, and radioimmunodetection may well serve to be an important method for diagnosing a variety of cancers in the near future. Immunotherapy is actively being explored in a number of centers but at this stage is strictly experimental. Whether this will be an important addition to our therapeutic armamentarium should be defined over the next several years. The monoclonal antibodies that are currently used for clinical studies are murine, that is, they are mouse antibodies. Although these antibodies have been well tolerated in a number of studies, human monoclonal antibodies would be theoretically more desirable. Preliminary efforts to produce human monoclonal antibodies reactive with tumor-associated antigens have been reported. Future directions of monoclonal antibody technology will employ greater production of human monoclonal antibodies. In addition, the evaluation of antibody conjugates for clinical diagnosis and therapy will continue to be explored.