To assess efficacy and safety of BeneFix® for prophylaxis in "Short-term" therapy and on demand therapy for all bleeding episodes of subjects with hemophilia B.

Phase IV, open-label, non comparative, multicenter, previously treated patients (PTP) clinical trial. Patients with severe or moderate hemophilia B with baseline levels of plasma factor IX < 5% activity will participate in this study for both treatment regimens: "on demand" therapy for acute bleeding episodes and therapy for prophylaxis of bleeding episodes ( "Short-term therapy")*.

* Short-Term Therapy: Prophylactic therapy given before surgery, including dental procedures, prior to a event that would likely result in bleeding ( sports, exercise, or heavy work), as well as to prevent further bleeds into a target joint). This short-term therapy for intermittent secondary therapy.

Inclusion Criteria:

1. Patients with moderate to severe hemophilia B ( < 5% circulating factor IX activity) having acute hemorrhage or requiring "short-term therapy" for intermittent secondary prophylaxis regimens.
2. HIV seropositive ( asymptomatic) or seronegative subjects.
3. No history or detectable inhibitors.