The purpose of this study is:

• to compare the pharmacokinetics of Replenine®-VF and Replenine® or any other high purity Factor IX concentrate, when given as a bolus dose of 75IU/kg.
• to compare the 1st and 2nd pharmacokinetic assessments on Replenine®-VF (conducted 3 months apart) and recovery if patients changes batches.
• to evaluate Replenine®-VF in terms of clinical tolerance and safety in patients with severe haemophilia B.

Inclusion Criteria:

• Patients aged 12 years or over
• At least 20 exposures suffering from severe Haemophilia B and without inhibitors to Factor IX and on Replenine® or any other high purity Factor IX product

Exclusion Criteria:

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