OBJECTIVE The pharmacokinetic (PK) study of recombinant human factor IX (rFIX) has been done in patients with hemophilia B in areas other than Taiwan. However, wide patient-related variability in recovery is noted and there is no PK study of rFIX in Taiwanese patients with hemophilia B. The purpose of this study is to evaluate the PKs of the rFIX in Taiwanese patients with hemophilia B. METHODS A PK study of rFIX was performed in 10 previously treated Taiwanese patients with hemophilia B. Nine of them had severe hemophilia B and the other one had moderately severe hemophilia B. The mean age of our patients was 24.7 +/- 8.6 years (mean +/- SD) with a range of 15.5-47.0 years. RESULTS The infusion of 75 IU/kg of rFIX in our patients resulted in a mean FIX activity increase of 1.08 +/- 0.27 IU/dL per IU/kg with a range of 0.3-1.49 IU/dL per IU/kg, and a mean in vivo recovery of 44.0 +/- 9.5% with a range of 31.4-60.4%. The mean elimination half-life was 24.4 +/- 6.4 hours with a range of 14.1-35.3 hours. The mean values of area under the curve, total body clearance, volume of distribution at steady state were 1363 +/- 166 IU x hour/dL, 4.84 +/- 1.03 mL/hour/kg, and 144.3 +/- 41.8 mL/kg, respectively. In addition, rFIX was well tolerated in our patients. Only two patients experienced mild treatment-related adverse events, including fever and feeling sleepy, respectively. Both of them resolved spontaneously without any sequences, and there was no thrombosis formation or inhibitor development in the following 6 months after rFIX infusion. CONCLUSIONS The results of PK study of rFIX in our previously treated Taiwanese patients with hemophilia B are comparable to the reported results from other related studies conducted in different geographical areas.