George T. Bryan, M.D., Ph.D., is Professor of Human Oncology at the University of Wisconsin Center for Health Sciences, and Clinical Consultant, William S. Middleton Veterans Administration Hospital at Madison, Wisconsin.Samuel M. Cohen, M.D., Ph.D., is a Professor and Vice-Chairman of the Department of Pathology and Laboratory Medicine and Professor of the Eppley Institute for research in Cancer and Allied Diseases at the University of Nebraska Medical Center in Omaha, Nebraska.