A chromogenic kit for the photometric determination of factor VIII activity in plasma, such as when identifying factor VIII deficiency or monitoring patients on replacement therapy as well as for potency estimation of FVIII concentrates. Fulfills the requirements of the European Pharmacopoeia for factor VIII concentrate testing. Co-lyophilization of reagents for convenient handling. Reliable tool for hemophilia classification. No interference from heparin levels up to 1.5 IU/mL. The Factor VIII kit has two measuring ranges plus validated and documented protocols for a wide range of instruments.