L-threonine deaminase was obtained at a high degree of purity from rat liver. Two main steps were added to the previously reported procedure: cryoprecipitation and chromatofocusing (in the presence of a specific KCl concentration). The purification factor was 3,090 and the specific activity 989. The method is very reproducible and convenient. It gives the highest specific activity and the highest degree of purity of the enzyme recorded to date.