PETER D. WALZER is Chief of the Division of Infectious Diseases at the Cincinnati Veterans Administration Center, and Professor of Medicine as well as of Pathology and Laboratory Medicine at the University of Cincinnati College of Medicine in Cincinnati, Ohio. An authority on Pneumocystis carinii pneumonia, he has published nearly 100 articles, book chapters, and proceedings papers, and he has presented numerous papers at conferences throughout the U.S. He is a Fellow of the American College of Physicians and Infectious Disease Society of America, and he is a member of the American Society for Microbiology, American Society of Tropical Medicine and Hygiene, American Society of Parasitologists, American Thoracic Society, American Association of Immunologists, and others. Dr. Walzer received the B.S. degree (1964) from Boston College and M.D. degree (1968) from Albany Medical College in Albany, New York. ROBERT M. GENT A is Associate Professor of Pathology and Laboratory Medicine at the University of Cincinnati College of Medicine and a Staff Pathologist at the Veterans Administration Medical Center in Cincinnati, Ohio. He is the author or coauthor of some 40 articles and book chapters, many of them concerning his research specialty in Strongyloides stercoralis. Among the professional societies he belongs to are the College of American Pathologists, American Public Health Association, American Society of Tropical Medicine and Hygiene, American Society of Parasitologists, and New York Academy of Sciences. Dr. Genta received the M.D. degree (1971) from the University of Turin Medical School in Italy and a diploma (1977) from the University of Liverpool's Liverpool School of Tropical Medicine in the U.K.