A nucleus colony of dogs with congenital coagulation and platelet function defects is maintained for breeding purposes, genetic and physiologic studies, production of reagents for coagulation tests, and evaluation of hemostasis. Dogs with hemophilia A, hemophilia B, hemophilia AB, von Willebrand's disease, factor VII deficiency, factor X deficiency, factor XI deficiency thrombasthenic thrombopathia, and various combinations of these defects are kept. A breeding colony of fawn-hooded rats with hereditary platelet serotonin deficiency (storage pool disease) is maintained for studies of the analogous human disease. A new hereditary canine platelet function defect is being studied. Isolated organ perfusion studies with rabbits are providing information about the organs and cellular sites involved in the production, regulation and release of coagulation factors. Heterologous antibodies to purified rabbit and canine factor VIII are used to monitor factor VIII antigen levels in the organ perfusion studies and in the dogs with various single and multiple coagulation defects. Studies of canine von Willebrand's disease are directed at the nature of its bleeding time and platelet adhesiveness defects.