Basic fibroblast growth factor (bFGF) is a multifunctional protein that stimulates proliferation, migration and differentiation of various cell types of the mammalian brain. In rat astrocyte cell cultures bFGF stimulates DNA synthesis after exogenous addition. This article will focus on the endogenous pathway of bFGF in rat astrocytes in cell cultures. After a single administration of bFGF antisense phosphorothioate oligodeoxynucleotide (PTO) a significant inhibition of DNA synthesis was observed. A control oligodeoxynucleotide does not inhibit DNA synthesis, while specific antisense c-myc PTO did inhibit DNA synthesis. Addition of anti bFGF PTO suppresses the expression of bFGF protein in Western blot analysis. These results suggest that bFGF may be an endogenous growth signal in developing astrocytes.