Unfractionated pure ferritin isolated from the livers of female or male mice forms five narrow protein-positive bands on standard 5% polyacrylamide gel disc electrophoresis (pH 9.0). Since all of these sub-bands also contain iron, they are interpreted as being isoferritins. The multiple sub-bands are very unlikely to be artifactually generated by the analytical procedure used since they are not found in horse spleen ferritin when this is coelectrophoresed with female mouse liver ferritin. The present results provide an independnet indication that many isoferritins indeed can be found within a single organ.