This prospective, multicentre, open-label study evaluated the efficacy and safety of a plasma-derived factor IX concentrate [Mononine, Coagulation Factor IX (Human) Monoclonal Antibody Purified] administered by continuous intravenous (CIV) infusion to patients with haemophilia B. Admission criteria included documented diagnosis of haemophilia B (mild, moderate, or severe). Twenty-eight patients (25 surgery, two trauma, one severe spontaneous haemorrhage) were enrolled to receive a therapeutic bolus dose followed by CIV infusion of factor IX (FIX) to maintain FIX:C plasma levels of 0.4-1.0 IU mL(-1) (i.e. 40-100%). A median intravenous bolus dose of 54.2 IU kg(-1) FIX was administered to a subset of 13 non-emergency patients 7-21 days prior to CIV infusion to determine pharmacokinetic parameters in order to guide the dosing for CIV. For treatment, a bolus injection (median FIX dose; 89.6 IU kg(-1)) (range, 12.4-108.3), followed by a median total CIV infusion dose of 396.4 IU kg(-1) (range, 44.9-785.5) was administered at a median rate of 3.84 IU kg(-1) h(-1) (range, 1.74-7.33) for 107.17 h (range, 31.75-144). Twenty-four patients completed 72-120 h of FIX CIV infusion. Overall, 'excellent' (i.e. achievement of normal haemostasis) efficacy was reported in 23 of 24 (96%) evaluable patients, and 'good' (i.e. slight oozing) efficacy was reported in one (4%) patient. Median FIX:C was 72-86% for all patients receiving FIX by CIV on all days. Nine patients reported 13 adverse events that were possibly related to study medication but were not deemed serious by the investigator and were mainly because of local irritation at the infusion site. FIX CIV infusion therapy is safe and effective in the treatment of haemophilia B patients undergoing surgery, exposed to trauma, or experiencing severe spontaneous haemorrhage.