W ITH THE ADVENT of modern vaccines, diseases such as smallpox, poliomyelitis, and diphtheria are now essentially preventable. Although a confirmed indigenous case of smallpox has not been reported in the United States since 1949 according to the Surveillance Section of the Public Health Service's Communicable Disease Center, cases of diphtheria and poliomyelitis continue to occur. In 1965, 160 cases of diphtheria and 59 of poliomyelitis were reported to the Communicable Disease Center (1). Persons with such illnesses, especially prior to diagnosis, obviously present a serious threat to others. Certain persons within the community who are especially subject to exposure to communicable diseases are considered members of high-risk groups. Foremost among these are physicians, dentists, nurses, hospital personnel, and ambulance attendants (2). Persons with irregular or limited exposure to patients, such as laundry handlers, cooks, and hospital carpenters, have also contracted disease as a result of their indirect contact with hospitalized patients. This threat to others from persons with communicable diseases was demonstrated in Great Britain in 1961-62 when several people with smallpox, accidently admitted into the country, infected 62 other persons, resulting in 26 deaths. Of these, 40 cases and 21 deaths occurred in 3 physicians, 1 nurse, 2 hospital visitors, 33 hospital patients, and 1 hospital employee (3). Analysis of 11 serious outbreaks, of smallpox following importation into Europe since December 1961 reveals that 96 of 222 indigenous cases and 29 of 39 deaths occurred among persons known to have acquired the disease directly through hospital contact (4). When a patient suspected of having smallpox was recently admitted to a Washington, D.C., hospital, health officials were reawakened to the vast problems involved when such a disease is introduced into a susceptible population (5). For this reason the American Medical Association, the American Hospital Association, and the Public Health Service recommend that hospital personnel keep current their immunizations against smallpox (personal communication, J. D. Millar, Smallpox Surveillance Section, Communicable Disease Center, March 1965). Hospital personnel may also be considered vulnerable to other infectious diseases, such as Dr. Sells, formerly epidemic intelligence service officer, Kansas City Field Station of the Public Health Service's Communicable Disease Center, is now a resident in pediatrics at the Children's Orthopedic Hospital and Medical Center, Seattle, Wash. Dr. Lyman is health director of the Omaha-Douglas County Health Department in Omaha, Nebr., and Mr. Kirby, formerly immunization project coordinator, assigned to the Omaha-Douglas County Health Department by the Public Health Service, is presently assigned to the California State Department of Health.