Primary cultures from newborn rat cerebral cortex, striatum, hippocampus, brainstem and cerebellum were grown for 14 days. There was a linear relationship between the amount of material seeded and the protein content of the respective culture. The amount of tissue material seeded was selected so that the different cultures reached confluence at 6-7 days and contained similar amounts of protein when 7 and 14 days old. The cellular content was evaluated by astroglial markers, such as the glial fibrillary acidic protein (GFAp; alpha-albumin) and the S-100 protein, and by markers for other cells expected to be in the cultures (14-3-2 protein, macrophage acidic protein (MAP), alkaline phosphatase, myelin basic protein (MBP), 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP]. Astroglial-like cells represented 60-70% of the cells present in the different cultures. Quantitation of GFAp (alpha-albumin) showed similar amounts to be present in cultures from cerebral cortex, hippocampus and striatum; however, on lower levels expressed in soluble proteins than in the corresponding brain regions of adult rats. Brainstem of adult rat contained large amounts of GFAp (alpha-albumin), while low levels were found in brainstem culture. Also, phagocytic cells (macrophages), endothelial-like cells, mesenchymal-like cells, ependymal-like cells and oligoblasts were found. Neither mature neurons, nor oligodendroglial cells were observed. It is concluded that although there might be some differences in the degree of maturation or in the cellular composition of the various cultures, they could serve as a good model system for studying the characteristics of astroglial cells from various brain regions.