Morbidity and mortality from infectious diseases clearly remain high. Economic assessments should not be based soley on the costs of existing disease but should incorporate costs saved by preventive efforts as well as savings likely to be attained within several years by improved preventive measures. These factors can be used to assess the relative needs for research for specific infections and to compare the economic importance of infections with that of other health problems. Preventive activities for individuals and for larger groups are outlined, and the relation of research to prevention and control of infections is presented.