Since S-2337, which is included in the Coatest FX kit, is not available for separate purchase, another substrate must be employed. S-2765, which is also a substrate for FXa, can therefore be used, and a method based on the activation of FX in the presence of calcium using Russell’s Viper Venom (RVV) as the activator is described in the Chromogenix catalog. DiaPharma has composed a new DiaPharma Factor X kit for research use only based on S-2765.