BACKGROUND Recovery and half-life estimations were carried out to compare a high-purity factor IX concentrate with an established factor IX complex concentrate. METHODS Two high-purity factor IX concentrates, which are identical except for the presence or absence of heparin (Immuninehep-plus and Immuninehep-minus), were evaluated in two independent crossover studies using an intermediate-purity factor IX complex concentrate (Bebulin) as reference drug. RESULTS In the Immuninehep-plus crossover study (n = 27), Immuninehep-plus and Bebulin had, respectively, a recovery of 0.90 +/- 0.26 and 0.84 +/- 0.23 IU per dL per IU per kg, a compartmental half-life of 17.11 +/- 6.18 and 15.94 +/- 4.69 hours, and an effective half-life of 16.51 +/- 3.48 and 16.48 +/- 4.26 hours. In the Immuninehep-minus crossover study (n = 26), Immuninehep-minus and Bebulin had, respectively, a recovery of 0.92 +/- 0.31 and 1.02 +/- 0.36 IU per dL per IU per kg, a compartmental half-life of 17.42 +/- 5.60 and 18.77 +/- 6.27 hours, and an effective half-life of 16.39 +/- 4.44 and 16.48 +/- 4.28 hours. Equivalence tests indicated that the recovery and half-life of Immunine, with or without heparin, are equivalent to those of Bebulin. CONCLUSIONS The equivalence in pharmacokinetics and bioavailability indicates that the dosage schedule for Immunine should be the same as or very similar to that of Bebulin. The high specific activity of the former, however, allows administration at lower volumes.