1 This symposium was held at the Fifty-sixth General Meeting of the Society of American Bacteriologists at Houston, Texas, May 3, 1956. Professor William G. Walter, Montana State College, Bozeman, Montana, served as secretary. Participants were: R. E. Buchanan, Iowa State College, Ames, Iowa; Margaret Pittman, National Institutes of Health, Bethesda, Maryland; Sidney Leopold, Fort Detrick, Frederick, Maryland; Charles D. Dukes, Baylor University College of Medicine, Houston, Texas; Reese H. Vaughn, University of California, Davis, California; Eric R. Brown, University of Kansas, Lawrence, Kansas, and Fellow, National Cancer Institute; E. Lee Treece, University of Kansas, Lawrence, Kansas; Kenneth L. Burdon, Baylor University College of Medicine, Houston, Texas; C. W. Hesseltine, Northern Utilization Research Branch, Peoria, Illinois; and N. M. McClung, University of Kansas, Lawrence, Kansas.