In glial cell cultures from newborn rat hemispheres we have demonstrated by immunocytochemistry the presence of carbonic anhydrase (CAII) and glial fibrillary acidic protein (GFAP) in the same cell. These double-stained cells are detected between day 5 and day 13 after seeding. These cells could be morphologically identified as oligodendroblasts. At 5 days in culture about 10% of the cells containing CAII also contained GFAP. At 11 days only 2% preserved this property. After 13 days in culture GFAP was only localized in typical astrocytes and CAII in oligodendroglial-like cells. The presumption that the immature glial cells, which contained specific markers of astrocytes and oligodendrocytes, became in our culture conditions essentially oligodendroglial cells is discussed.