Recombinant factor VIIa (rFVIIa) (NovoSeveng) is used to treat bleeding episodes in hemophilia A and B patients with inhibitor antibodies against factor VIII (FVIII) and factor IX. rFVIIIa has been studied in home treatment of mild-to-moderate joint, muscle, and mucocutaneous bleeds to assess safety and efficacy. Treatment with other factor concentrates was allowed according to treating physician's judgment. Blood samples were drawn before study start and after 6 and 12 months. It has thus been possible to follow the inhibitor titres during this period. Analyses of 53 patients (49 hemophilia A, four hemophilia B) showed inhibitor levels up to 1,208 BU/ml before study start. Based on the first analysis, hemophilia A patients were divided into high responders (> 5 BU/ml; 28 patients), low responders (> 1 and < 5 BU/ml; 15 patients) and very low responders (< or = 1 BU/ml; six patients). In high responders receiving rFVIIa as only treatment, FVIII inhibitor titre decreased to one-third of the initial level. For high responders receiving other factor treatments such as FVIII or prothrombin complex concentrates, inhibitor titre remained unchanged. Titres for low responders and very low responders remained unchanged independent of treatment. Thus, when rFVIIa is used as the only coagulation factor to treat hemophilia A/B high-responder inhibitor patients, inhibitor level declines significantly.