A long-standing concern for international spread of new, virulent pathogens became a reality with the advent of Severe Acute Respiratory Syndrome (SARS). This respiratory syndrome, caused by a coronavirus, spread rapidly across 30 nations since its first recognition in late 2002. SARS has presented the greatest recent threat to U.S. public health, and has come at a time when purposeful introduction of pathogens by terrorists is also of heightened concern. SARS has forced the international medical establishment to reexamine how best to manage such incidents.