Substantial amounts of biologically active FVIII are present in human prenodal and mouse thoracic or cyst lymph. Lymph was collected as described in the text, and FVIII:C activity was measured by using the Biophen FVIII:C Kit. The data represent FVIII:C activities of individual lymph samples relative to that of human or mouse pooled normal plasma level of FVIII (defined as 100%) as described in “Materials and methods.”