1. A new procedure is described for the isolation of pure ferritin from small amounts of tissue. After the removal of most of the tissue proteins by heat coagulation, the ferritin fraction was chromatographed successively on CM-cellulose and Sephadex G-200. 2. The isolated ferritin appeared to be free from other proteins, as judged by its sedimentation pattern in the ultracentrifuge, by electrophoresis on polyacrylamide gel and by immunoelectrophoresis. 3. After the injection of [(14)C]leucine into a series of rats, the specific activity of liver ferritin isolated by the new procedure bore a constant relationship to that of liver ferritin separated by antigen-antibody precipitation. The procedure can thus be used to obtain ferritin of suitable purity for studies of amino acid incorporation. 4. The new procedure can be used to measure the total ferritin protein content of a tissue. It is not possible to use ultraviolet absorption for the measurement of ferritin protein because of considerable interference from the iron that it contains.