Minimally destructive methods were sought to assess the factor VIII content of fresh frozen plasma intended for large-scale fractionation and stored in five-liter polyethylene packs after pooling approximately 23 plasma donations. Although factor VII distribution in the frozen pack was not perfectly homogenous, a central "core" through the frozen pack gave a representative sampel of the entire contents of the pack. Coring was compared with other methods of pack sampling before large-scale cryoprecipitation. The survival of factor VIII was studied in three grades of stored plasma which had been separated and frozen within 4 hours, 8 hours, and 18 hours of blood donation. Plasma frozen after overnight storage of blood is a satisfacory starting material for the preparation of factor VIII and factor IX concentrates.