Acidic fibroblast growth factor (aFGF) could stimulate the proliferation of astrocytes and promote the survival of neurons from newborn rat brain in vitro. The effects of aFGF on both astrocytes and neurons were significantly potentiated by heparin. The effect of aFGF (2 ng/ml) with heparin (10 mu g/ml) on the survival of neurons was a hundredfold more potent than that of aFGF (200 ng/ml) without heparin.