Haemophilia is a bleeding disorder characterised by a deficiency in Factor IX. Replacement therapy in the form of a Factor IX concentrate is a widely accepted practice. In this paper we describe a double virus inactivated chromatographic process for producing a high purity Factor IX product, MonoFIX(®)-VF. The process involves separation of the prothrombin complex by cryoprecipitation, fraction I precipitation and DEAE-cellulose adsorption, further ion-exchange chromatography of crude Factor IX, followed by solvent/detergent treatment. Heparin affinity chromatography is then used to further purify Factor IX. Final nanofiltration is sequential through 35 nm then 15 nm membrane filters. The principal virus inactivation/removal steps are solvent/detergent treatment and nanofiltration and the partitioning of relevant and model viruses provides further reduction in virus load through the production process.Solvent/detergent treatment was shown to achieve log reduction factors of 4.5 for HIV-1, 5.1 for Sindbis virus, 6.1 for vesicular stomatitis virus (VSV), 5.1 for bovine viral diarrhoea virus (BVDV) and 5.3 for pseudorabies virus (PRV). BVDV is a model for hepatitis C virus (HCV), and pseudorabies virus (PRV), like hepatitis B virus (HBV) is an enveloped DNA virus. Using scaled down models of the production process, we have also demonstrated the neutralization/partitioning of at least 6 logs of hepatitis A virus (HAV) during cryoprecipitation, Fraction I precipitation, and the DEAE adsorption and elution step, and a further 1.6 log reduction in HAV load as a result of heparin affinity chromatography. The log reduction factors for HAV as a result of the second ion-exchange chromatography step and as a result of enhanced neutralisation associated with solvent/detergent treatment were not significant. Nanofiltration was shown to contribute a further log reduction factor of 6.7 for HAV and 5.8 for BVDV indicating that log reduction factors of this order would be obtained with other viruses of a similar or larger size, such as HIV, HBV and HCV.Overall, these studies indicate that MonoFIX-VF is a product with an extremely high level of viral safety.