Around 20 years ago, a mother admitted her hemophilic son, 1% years of age, knowing that he had an inhibitor, to our center by ambulance. He showed severe bleeding episodes into his right shoulder, right upper arm and right chest. The inhibitor titer at that time was:> 500 Bethesda units (BU). Some months earlier, in 1974, we had heard about a publication by Kurczinsky and Penner [I] about the successful treatment of bleeding episodes in patients with an inhibitor with activated prothrombin complex concentrates. When calling a manufacturer (Immuno), asking for a similar product, we were told that this was still in development, and not available at the moment. In this serious situation, we decided to combine high dosages of factor VIII with a regular prothrombin concentrate. This regimen was given twice a day to the patient, and the bleeding could be controlled. After 3 weeks the patient recovered completely, and he could be dismissed from the hospital. Astonishingly, during this treatment the inhibitor titer decreased to slightly more than 40 BU. Therefore, it appeared to be reasonable to evaluate this procedure also in other hemophilic patients with an inhibitor suffering from acute bleeding episodes. We observed that in some patients there was a booster effect on the inhibitor, and in some not, but the inhibitor titer decreased in all cases after some weeks of treatment. We decided not to stop the treatment, but to continue this procedure, and realized that the inhibitor finally disappeared. Subsequently, al-so the half-life of factor VIIl normalized. However, it took around 2 years to develop the dosage schedule that we are using today.