Biological weapons are natural organisms or diseases used in a harmful or destructive manner (e.g., smallpox, anthrax, and Ebola). Many countries and terrorist groups have the capability of mass producing lethal viruses and distributing them throughout the human population. The pervasiveness of the U.S. civil aviation presence in the world, combined with the vulnerable state of aviation preparedness in combating and responding to biological attacks, creates a significant risk to airports, air carriers, and the American public. During a suspected biological attack, the public health community will have a major role, because it has a more comprehensive understanding of the problem. The Centers for Disease Control and Prevention (CDC), together with local and State health authorities, will assume part of the decisionmaking process; in noncriminal cases, they may even take the lead. Some of the questions that must be answered before an outbreak of disease can be considered criminal are posed in this article. Only interagency cooperation will ultimately determine whether a biological event requires a criminal investigation. Given the need for trained and expert guidance, the emergency operations center (EOC) may become a unified command post responsible for managing the biological crisis. The EOC gains input via a team of firefighters, medical personnel, police, and airport and air carrier representatives, any of whom could become the key decisionmakers when the need arises. Carrying out a cooperative strategy assumes a high level of training in unified command procedures and a strong partnership with local, State, and Federal public health entities. Tabletop exercises should evolve into planning for full-scale exercises. Air carriers also have a role in defending against these types of incidents beyond their involvement in exercises. Airplane crew training should include information about WMD. Personnel should know what procedures to follow if a biological event occurs, and airlines should develop and implement means to assist with passenger tracking after the conclusion of flights. The entire civil aviation community should establish both preventive and countermeasures against WMD. National-level procedures that focus on "best-risk" airports into which flights may be diverted should be considered. Additionally, partnership opportunities across the civil aviation spectrum should be explored. 9 notes