Ferritin in 119 astrocytoma cases was studied by immunocytochemical PAP and immunogold silver staining (IGSS) methods. In 57% of the cases, ferritin was found in the cytoplasm of the tumor cells. The higher the differentiation of the tumor cells, the less ferritin they contained. Contrary to the reaction of glial fibrillary acidic protein (GFAP), the positive rate of ferritin in various types and grades of astrocytomas was inversely proportional to their degree of differentiation. Electron microscopic observation in 30 cases showed ferritin in the cell sap, cytocavity network, endoplasmic reticulum, Golgi apparatus and also in lysosomes. Some of the cases had extraordinary high level of ferritin in their blood serum.