A new, high-potency, glycine-precipitated antihemophilic factor (AHF, factor VIII) concentrate, from 100 to 400 times purified, can be administered to patients in solutions 100 times more concentrated than plasma. The product appears to be stable and causes no immediate untoward side reactions. The plasma AHF levels of patients with classical hemophilia can be normalized with small volumes of the glycine-precipitated material given by syringe. Surgery can be performed safely under cover of this fraction. Two patients with classical hemophilia complicated by a circulating inhibitor to AHF were treated with large amounts of the high-potency fraction; partial to complete neutralization of the inhibitor occurred with clinical improvement.