Lactate dehydrogenase M4-isoform in the homogeneous state was isolated from the rat liver by successive application of sulphate-ammonium fractionation, phosphocellulose ion-exchange chromatography with high-affinity elution of 1 mM NADH and subsequent hydroxyl apatite fractionation. The method permits obtaining the preparation amounts of the enzymic protein with yield 37.5%, specific activity 386.8 units per 1 mg of protein. It is established that 1 mM NAD+, 10 mM pyruvate and 100 mM lactate are also effective as agents of the selective enzyme elution.