We describe a young woman who developed acquired haemophilia after 18 months of interferon (IFN-)-alpha therapy. This patient had been monitored since 1992 for Hodgkin's disease initially treated by chemotherapy. After two relapses, she received intensive chemotherapy followed by an autologous peripheral progenitor cell graft. IFN-alpha was then administered for 18 months. Bleeding of the limbs and tongue occurred 1 month after withdrawal of IFN-alpha and high titres (123 Bethesda units) of autoantibody to factor VIII (FVIII):C were measured. Prednisone (1 mg kg(-1) day(-1)) achieved rapid cessation of the bleeding and FVIII autoantibodies were undetectable 5 months later. This case report suggests that the activated partial thromboplastin time should be regularly checked in every patient treated with IFN-alpha in cases of unexplained bleeding, together testing for antibodies to FVIII if the bleeding is prolonged.