This conference was held under the sponsorship of the Eastern Pennsylvania Branch of the American Society for Microbiology, as one in a continuing series of Basic Science Symposia. The untiring volunteer effects of the members of the Symposium Committee are deeply appreciated. The Bureau of Laboratories of the Pennsylvania Department of Health was a cosponsor and generously provided staff and secretarial services to handle the difficult task of registration. The Department of Microbiology and of Microbiology and Immunology at the five medical schools in Philadelphia -- Temple University School of Medicine, Medical College of Pennsylvania, Thomas Jefferson University, Hahnemann University and the University of Pennsylvania -- were academic cosponsors, and the support of the Chairpersons and the faculties are gratefully acknowledged.