The Centers for Disease Control and Prevention (CDC), Coordinating Center for Infectious Diseases (CCID), intends to negotiate a sole source purchase order with Acambis, Inc.(also known as Sanofi Pasteur), under the authority of FAR 6.302-1, Only One Responsible Source and No Other Supplies or Services will Satisfy Agency Requirements. The contractor shall perform potency testing using the Food and Drug Administration (FDA) qualified and validated vaccinia based potency assay on samples of Wetvax provided by the CDC. CDC has an agreement with the FDA to perform yearly testing of the Strategic National Stockpile (SNS) Aventis Pasteur Smallpox Vaccine.