In 1998, the State Department established the worldwide voluntary anthrax immunization program based on a general assessment of chemical and biological threats to United States’ interests overseas. This assessment did not evaluate the relative risk of chemical and biological attacks on each potential target, identify the chemical and biological agents likely to be used, or assess the ability of states or terrorist groups to disperse the agents and cause mass casualties. As a result, the extent to which U.S. overseas missions were vulnerable to chemical and biological attacks was uncertain. Therefore, the basis for the State Department's worldwide anthrax vaccine immunization program is questionable. In addition, the State Department’s efforts to immunize its employees and their dependents were poorly implemented. Most of the vaccine was not used or was redistributed for use elsewhere and had to be destroyed upon its expiration date. None of the anthrax vaccine recipients in the pilot program received the full series of vaccinations. Adverse reactions could have been underreported because passive, rather than active procedures were used to monitor reactions. Because the vaccine was in short supply, the State Department suspended expansion of its vaccination program to other U.S. missions overseas. Some recommendations to the State Department in the event that the vaccination program is resumed are: to determine whether a voluntary vaccine immunization program is the most effective approach to protecting U.S. personnel overseas; and require that appropriate vaccine storage and redistribution mechanisms are in place before anthrax vaccine is shipped overseas. 2 tables, 17 notes, and 2 appendices.