In 1980, the World Health Organization (WHO) officially declared that smallpox had been eradicated. In 1986, WHO's international Ad Hoc Committee on Orthopox Virus Infections unanimously recommended destruction of the two remaining official stocks of variola virus, one at the Centers for Disease Control and Prevention and the other at the VECTOR laboratory in Siberia. In June 1999, WHO decided to delay the destruction of these stocks. Informing that decision was Assessment of Future Scientific Needs for Variola Virus, which examines: -- Whether the sequenced variola genome, vaccinia, and monkey pox virus are adequate for future research or whether the live variola virus itself is needed to assist in the development of antiviral therapies. -- What further benefits, if any, would likely be gained through the use of variola in research and development efforts related to agent detection, diagnosis, prevention, and treatment. -- What unique potential benefits, if any, the study of variola would have in increasing our fundamental understanding of the biology, host-agent interactions, pathogenesis, and immune mechanisms of viral diseases.