Purified from freshly collected bovine plasma using a combination of salt precipitations and column chromatography. This protein is a mixture of Factor V/Va and intermediate activation products as judged by 4-20% gradient gels. Bovine Factor Va functions as a cofactor with the serine protease Factor Xa in the activation of prothrombin. This protein may be used as a source of V/Va in the Prothrombinase complex.