During the last two decades major advances have been achieved in the management of haemophilia. Modern approaches aimed at preventing the recurrent bleedings and their sequelae have been widely adopted. Major challenges of intensive treatment regimens employed today, such a short half life of haemophilia therapeutics with a need for frequent injections and the risk of inhibitor, encourage further development towards the production of factor concentrates with prolonged efficacy and reduced immunogenicity. Intensive research work on gene therapy aimed at ultimate cure of haemophilia by the restoration of missing factor FVIII (FVIII) and factor IX (FIX) production is ongoing. The current issues of gene therapy and mechanisms, modifying the host immune response to the FVIII and FIX transgene material and the coagulation factors expressed are the topic of the Arosenius lecture by Katherine High. Despite an extensive research on mechanisms leading to inhibitor development, the real reason of these serious complications of haemophilia therapy still remains unclear. Alessandro Gringeri will discuss the immunogenicity of plasma derived FVIII (pd FVIII) and recombinant FVIII (rFVIII) concentrates as one of potential, treatment related, and probably 'modifiable' risk factors for inhibitor development. The SIPPET study--a new prospective, randomised study aimed to reveal real incidence of inhibitors in patients treated with either pdFVIII or rFVIII will be presented.