Treatment of the bleeding disorder hemophilia in the nineteenth century was empirical, based on clinical experience. Medications, transfusions of human or animal blood, and injections of blood sera were utilized in an attempt to halt life-threatening hemorrhages. After 1900, the application of clinical laboratory science facilitated the utilization of anti-coagulated blood and donor blood compatibility tests for safer emergency transfusions. But repeated transfusions produced blood incompatibility that limited future utilization. Investigation of hormones and snake venom as coagulants appeared hopeful during the 1930s, but plasma globulin research during World War II resulted in the isolation of antihemophilic factors that promptly reduced hemorrhage. Their application to bleeding episodes resulted in a more normal life for hemophiliacs after 1950.