We report a new method to produce a solvent/detergent-treated and severe dry heat-treated factor VIII (FVIII) concentrate (3-6 IU FVIII:C/mg protein). This method, which uses a single purification step after cryoprecip- itation, is suitable for scale-up to production levels. FVIII was obtained from solvent/detergent-treated cryoprecipitate by a single gel filtration step using Sephacryl S-400HR. The freeze-dried product was stable to heating at 80°C for 72 h. The yield of the solvent/detergent and severe dry heat-treated product was 230 IU FVIII : C/kg plasma. The reconstituted product gave a 10% loss in FVIII : C activity after heating at 37°C for 6 h. The feasibility of this method suggests that gel filtration using S-400HR can be used solely or as part of a purification process for the preparation of high-purity FVIII concentrates.