The infusion of high purity Factor VIII and Factor IX concentrates represent one of the best alternatives in the treatment of haemophilia A and haemophilia B respectively. Among the dehydration techniques, freeze-drying is considered as the reference process preserving biological activity and, consequently, it is utilised for manufacturing high-quality pharmaceutical products. The aim of this work was to study the influence of the freezing and the drying conditions on the final quality of both freeze-dried high purity Factor VIII and Factor IX concentrates. The biological activity of both Factor VIII and Factor IX was not influenced by the freezing rates and. considering the experimental conditions that led to uncollapsed products, by the drying rates studied. Moreover, according to other previous works and to the industrial experience, no remarkable difference on their biological activities depending on the freezing and primary drying conditions was noticed for both factors. From these results, a new optimised cycle that permitted to reduce considerably the duration of the freeze-drying process, was defined. The freeze-dried products obtained had a relative biological activity in line with the actual industrial standards, were good rehydratable and showed a stability of at least 1 month at +4 C. (C) 2002 Elsevier Science B.V. All rights reserved.