The issues discussed are: (1) the extent to which data support the need for six initial shots and an annual booster of the anthrax vaccine; (2) the relative merits and weaknesses of a passive surveillance system in determining adverse events; and (3) the available data on differences in adverse reaction rates between men and women receiving the anthrax vaccine. Also discussed are the disadvantages of the current vaccine and the status of Federal efforts to develop an improved anthrax vaccine. Results of the investigation show that no studies have been done to determine the optimum number of doses of the anthrax vaccine. Although annual boosters are given, the need for this frequency and the amount of the booster dose has also not been evaluated. A passive surveillance system means that the Food and Drug Administration/Centers for Disease Control (FDA/CDC) must rely on vaccine recipients or their health care providers to report any adverse events after receiving the vaccine. Studies show that adverse events are reported significantly less than they would be in an active surveillance system. In an active system, generally more costly to administer, vaccine recipients are monitored to find out if they had any adverse events after being inoculated. Data from the Department of Defense’s efforts to determine adverse reactions show that women reported twice the rate of adverse reactions than men for both local (swelling) and systemic (malaise and chills) reactions. A higher proportion of women than men reported making an outpatient medical visit after a vaccination. More than twice the percentage of women reported that they missed one or more duty shifts after their vaccinations than did men. The disadvantages of the anthrax vaccine are (1) the amount of protective antigen cannot be precisely measured; and (2) the schedule and booster requirements complicate the logistics of inoculating all of the troops and increases the cost of the vaccine program. A second-generation vaccine with a more precise amount of protective antigen could be developed where fewer doses of the vaccine would be required. However, this has not been fully tested. 4 tables, 13 footnotes