The emphasis of immunization programs and schedules has traditionally been directed to infants and children, since most of the vaccine-preventable diseases are seen predominantly in these age groups. Immunization procedures in adults are less well defined but still of importance. Diseases for which immunizations are given before disease exposure include tetanus, diphtheria, influenza, rubella, and mumps; travelers to foreign countries may need immunizations against typhoid, cholera, yellow fever, typhus, poliomyelitis, plague, and viral hepatitis; other vaccines are available before disease exposure in unusual epidemiologic situations. After exposure to disease but before onset of symptoms, immunizations are available for rabies, viral hepatitis, and measles. After the onset of clinical illness, passive immunization should be given for tetanus, diphtheria, and botulism. This paper summarizes current practices for active and passive immunization against these diseases in adults.