While the exact risks are unknown, the use of biological weapons by terrorists potentially could result in life-threatening illness on a large scale. Even a lone terrorist could cause a major disease outbreak in the population - and, in the case of communicable disease, the outbreak could spread in successive waves of infection. Unlike explosions or chemical releases, a bioterrorist attack could be surreptitious and thus difficult and time-consuming to detect. Symptoms might not occur among victims for days or weeks, and those initially presenting themselves to physicians and clinics might be geographically dispersed. A strong public health network would be needed to piece together early reports and quickly determine what had happened. Once detected, the situation could overwhelm local health systems that are faced not only with the tasks of caring for mass casualties but also with the demands of even larger numbers of people requiring preventive care. In fiscal year 2001, HHS will invest $297 million in anti-bioterrorism efforts. HHS efforts are focused on five areas: improving the nation's public health surveillance network, to quickly detect and identify the biological agent that has been released; strengthening the capacities for medical response, especially at the local level; expanding the stockpile of pharmaceuticals for use if needed; expanding research on the disease agents that might be released, rapid methods for identifying biological agents, and improved treatments and vaccines; and preventing bioterrorism by regulation of the shipment of hazardous biological agents or toxins.