WITH the excellent antigenic materials now available a person and entire com¬ munities can be provided with virtually com¬ plete protection against historically important diseases such as smallpox, diphtheria, pertussis, tetanus, and poliomyelitis. Why, then, is im¬ munization with these antigens incomplete? Why isn't everyone immunized? The answer is complex and varies by time, place, person, and antigen. Obviously, because of great cultural differences and varied ex¬ periences with disease the extent of application of immunization differs greatly by country. Less obviously within the United States, the extent differs by State, county, city, and neigh¬ borhood according to community origins, ex¬ perience with disease, intelligence, education, wealth, and availability of immunization from public and private sources. But even under the best of circumstances in many of this country's most progressive communities, many people re¬ main unimmunized. Why? During recent years the authors and their coworkers have devoted considerable effort toward answering this question and toward im-Dr. Ravenholt is associate professor in the depart¬ ment of preventive medicine, University of Wash¬ ington School of Medicine. From 1954 to 1961 he was director of the division of epidemiology and communicable disease control, Seattle-King County Health Department. Mrs. Levinski is a research assistant, University of Washington, and Mrs. John¬ son, a public health nurse with the health department. Miss Ravenholt is now with the Department of State, U.S. Consulate, Recife, Brazil. provement of the immunization status and pro¬ grams of the Seattle-King County community. Therefore, this report of related findings and activities may be of value to others who are sim¬ ilarly engaged. Methods