BAX326 is a recombinant factor IX (rFIX; nonacog gamma) manufactured without the addition of any materials of human or animal origin, and with two viral inactivation steps (solvent/detergent treatment and 15nm nanofiltration). The aim of this prospective trial was to investigate the pharmacokinetics, haemostatic efficacy and safety of BAX326 in previously treated patients aged 12-65years with severe or moderately severe haemophilia B. BAX326 was safe and well tolerated in all 73 treated subjects; adverse events considered related to treatment (2.7% incidence, all non-serious) were transient and mild, and no hypersensitivity reactions, inhibitor formation or thrombotic events were observed. Pharmacokinetic (PK) equivalence (n=28) between BAX326 and a licensed rFIX was confirmed in terms of the ratio of geometric mean AUC(0-72h) per dose. Twice-weekly prophylaxis [mean duration 6.2 (+/- 0.7) months; 1.8 (+/- 0.1) infusions per week, 49.5 (+/- 4.8) IUkg(-1) per infusion] was effective in preventing bleeding episodes, with a significantly lower (79%, P<0.001) annualized bleed rate (4.2) compared to an on-demand treatment in a historical control group (20.0); 24 of 56 subjects on prophylaxis (43%) did not bleed throughout the study observation period. Of 249 total acute bleeds, 211 (84.7%) were controlled with one to two infusions of BAX326. Haemostatic efficacy at resolution of bleed was rated excellent or good in 96.0% of all treated bleeding episodes. The results of this study indicate that BAX326 is safe and efficacious in treating bleeds and routine prophylaxis in patients aged 12years and older with haemophilia B.