Severe hemophilia A (HA) patients develop inhibitory alloantibodies to factor VIII:C and therefore require bypass agents that are scarce, expensive and may provoke secondary effects. Twenty-three severe HA patients who were high-responders to FVIII inhibitors were studied. FVIII:C activity in plasma was measured by one-stage activated partial thromboplastin time method, and the quantification of FVIII:C inhibitors was carried out by the Nijmegen-Bethesda method. Inhibition kinetics was assessed through serial plasma dilutions. FVIII:C activity was