It has not as yet been routinely possible to derive primary cultures of glial cells from adult rat brain tissue even when adopting strategies that have proven successful with perinatal tissue. We now report that in response to a surgical lesion and a period of postoperative 'priming' in vivo, proliferating cultures of astroglial cells can be derived from the normally quiescent glia of the corpus callosum region of the adult rat brain. In such cultures the predominance of astroglia and the virtual absence of oligodendroglia and neurons has been established by the use of a variety of cell-type specific antisera. Fibroblasts, the only other cell type identified, when not numerous could be successfully eliminated by treatment of the cultures with anti-Thy-1 antibodies and guinea pig complement. Pure astroglial cells from adult brain have been sub-cultured and maintained for up to 4 months in vitro, providing suitable quantities of cells for studies on the trophic interaction between glia and neurons. In long-term culture the adult astrocytes maintain a flattened undifferentiated morphology but readily assume a stellate shape with long branching processes upon the addition of a crude homogenate from bovine pituitary.