The assurance of the safety for therapeutic agents derived from human plasma must include an evaluation of the clearance of known or unknown viruses by the production process. Similarly, for products produced by cell culture, the potential for the propagation of viruses during the cell culture process requires an assess­ ment of the risk incurred by the manufacturing process. Critical elements of the safety programs for products derived from both plasma and cell culture must include control and quality assurance of the starting materials. For plasma prod­ ucts, this will involve control over the plasma source, tracking of the donors, look-back procedures, and routine testing of the pooled plasma. For cell culture processes, the characterization of the cell bank, elimination or characterization of proteins or serum used in media, and postproduction testing for adventitious viral contamination all assure a consistent and safe product source.