Sufficiently early detection of a biological attack may be accomplished through surveillance schemes that can detect infected individuals earlier in the disease process. For completeness, we note that biosensors are being developed (and deployed) that detect organisms in the air and that this type of detection, if feasible, occurs fundamentally much earlier, because the delay introduced by the incubation period of the disease is eliminated from the surveillance system. 7 However, such approaches face unsolved technical problems in the analysis of contaminated specimens (the norm in air sampling). Biosensors also need to be in the right place-on every person's lapel or every street corner and hallway-to provide complete surveillance coverage.