The development of inhibitors in haemophilia patients is one of the most serious challenges to effective treatment. The effect of factor (F) concentrate and treatment regimen on titre levels was studied in nine patients with haemophilia A or B and inhibitors. Patients with haemophilia A were subdivided into those treated with recombinant activated factor VII (rFVIIa) on demand or those treated prophylactically with activated prothrombin complex concentrate (aPCC) and rFVIIa. A third group comprised haemophilia B patients receiving rFVIIa prophylaxis and on-demand aPCC or rFVIIa. On-demand therapy with rFVIIa proved to be effective and safe treatment for acute bleeding episodes in haemophilic patients. In group 1, inhibitor titres decreased markedly 0.5-21 months prior to immune tolerance therapy (ITT) and remained low for a further 1-19 months. However, use of rFVIIa instead of aPCC as prophylactic treatment in group 2 patients undergoing ITT failed to show favourable results for rFVIIa. This may be due to the short half-life of rFVIIa (2.3-2.9 h). The data presented suggest that exclusive use of rFVIIa in acute bleeding episodes prior to commencing ITT is an effective method of decreasing inhibitor titre, thereby optimizing conditions for ITT.