On 20 December 2001, the Centers for Disease Control and Prevention (CDC) initiated the Anthrax Vaccine and Antibiotic Availability Program (hereafter, the "Program") under an investigational new drug application with the US Food and Drug Administration. This Program provided options for additional preventive treatment for persons at risk for inhalation anthrax as a result of recent bioterrorism attacks who had concluded or were concluding a 60-day course of antimicrobial prophylaxis. Participants were offered an additional 40 days of antibiotic therapy (with ciprofloxacin, doxycycline, or amoxicillin) or antibiotic therapy plus 3 doses of anthrax vaccine. By 11 February 2002, a total of 5420 persons had received standardized education about the Program and 1727 persons (32%) had enrolled. Twelve participants have been identified as having serious adverse events (SAEs). One SAE, which occurred in a participant with ciprofloxacin-induced allergic interstitial nephritis, was considered to be probably associated with treatment received in the Program. No SAEs were associated with anthrax vaccine. CDC will continue to monitor Program participants during the next 2 years.