Concomitant use of the monoclonal antibody-purified factor IX concentrate (Mononine, Armour Pharmaceutical Company, Collegeville, Pa.) and two antifibrinolytic agents, ε-aminocaproic acid (EACA; Amicar, Immunex, Seattle, Wash.) or tranexamic acid (AMCA; Cyklokapron, Kabi Pharmacia, Pisca-taway, NJ.) was examined for safety and efficacy in patients with hemophilia B. In a retrospective review of 19 patients treated with monoclonal antibody-purified factor IX and EACA on 35 occasions, bleeding was successfully controlled and no instances of clinical thrombotic complications were reported; one instance of urticaria resolved without additional treatment. The use of EACA or AMCA in combination with monoclonal antibody-purified factor IX was also examined prospectively in a study of 9 patients. Bleeding was effectively controlled and no thrombotic events were detected clinically with either antifibrinolytic agent. No significant changes in hematocrit or hemoglobin were detected, and there was no evidence of thrombosis as evaluated clinically and by sensitive molecular markers. It was concluded from both the retrospective and prospective data that monoclonal antibody-purified factor IX concentrate in combination with an antifibrinolytic agent does not activate the coagulation cascade and is a safe and effective treatment for prevention and control of oral bleeding in hemophilia B patients.