1. A procedure for the isolation and purification of the heparin–protein complex from ox liver capsule, based on the solubility properties of mucopolysaccharide–cetylpyridinium complexes, is described. 2. The yield of the heparin–protein complex with this method averages 35mg./100g. of dry ox liver capsule. 3. The results of analyses on the polysaccharide show good agreement with values previously published for purified heparin fractions. 4. The amino acid analysis of the protein component shows several similarities to that of chondromucoprotein. 5. The results of β-carbonyl elimination, either with or without catalytic hydrogenation, and column chromatography after β-elimination, show that the polysaccharide is covalently bound to the protein.