Abstract: The present invention describes a process for activating Factor II to Factor II.sub.a by incubating Factor II in the presence of Factor V, Factor X.sub.a, phospholipids, and calcium ions. Each of the factors is prepared from a single impure protein fraction which includes Factors II, V and X. The Factor II, V and X purification procedure comprises the steps of DEAE ligand chromatography and precipitation by the addition of barium chloride. Factor V is recovered from the barium chloride supernatant, and Factors II and X are contained in the barium chloride precipitate. The barium chloride precipitate is dissolved in an aqueous solution and is applied to a chromatographic resin coupled with a ligand which binds Factor X and Factor II weakly or not at all. Factor II is recovered from the fraction, which remains unbound or weakly bound to the Factor X binding ligand. Factor X.sub.