One of the longest and most contentious policy debates in the field of international health has swirled around the fate of the last known stocks of variola virus, the causative agent of smallpox, which are held in 2 World Health Organization (WHO)-authorized repositories in the United States and Russia. After a global campaign under WHO auspices eradicated smallpox in the late 1970s, it was expected that the remaining laboratory samples of variola virus would be destroyed. In the mid-1990s, however, the U.S. government, concerned that a few countries may have retained undeclared caches of the virus for biological warfare purposes, sought to delay destruction of the WHO-authorized stocks in order to develop improved medical countermeasures. In 1996 the U.S. persuaded the World Health Assembly, the annual policymaking meeting of WHO member states, to approve the temporary retention of live variola virus at the 2 authorized repositories for an ambitious program of defensive research. Although in 1999 and 2002 the World Health Assembly extended the smallpox research program for additional periods until specified goals had been achieved, today pressures are growing to set a new date for virus destruction.