NIAID is playing a central role in the investigation of the disease known as Acquired Immunodeficiency Syndrome or AIDS. Research efforts directed toward the epidemiology, prevention, pathogenesis and treatment of the disease and its sequelae have intensified. The control of AIDS will require studies to understand the host immune system and its interactions with HIV and related retroviruses. Research to understand the biology of viral host interactions, to develop vaccines to prevent infection, to develop antiviral drugs to treat already infected individuals and to develop methods to boost or reconstitute the immune system will be assisted by establishing a series of standardized retroviral stocks for the scientific community. It is the purpose of this solicitation to support research activities of the scientific community and the AIDS Program by providing stocks of standardized HIV, SIV and related retrovirus stocks. Some virus stocks are available but the need for a centralized resource to provide these materials is essential. The NIAID needs access to significant quantities of the noted materials to support the efforts of the National Cooperative Drug Discovery Groups, the National Vaccine Developmental Groups, the AIDS Clinical Study Groups, the Programs of Excellence in Basic Research on AIDS, and other more specific programs initiated by NIAID.