The distribution in the rat nervous system of acidic and basic fibroblast growth factors (FGFs) was analysed by a combination of biochemical and anatomical methods. Acidic FGF (aFGF) was found to be present exclusively in specific neuronal populations, such as motor neurons and basal forebrain cholinergic neurons. Basic FGF (bFGF) was found in astrocytes and in neurons in hippocampal area CA2. Within labelled astrocytes and CA2-neurons, bFGF was detected in both the cytoplasm and the nucleus. The levels of intracellular bFGF were manipulated by antisense oligonucleotide treatment of cultures of developing neural crest cells. Results indicated that the amount of melanogenesis in the cultures is likely to be regulated by intracellular, possibly nuclear bFGF.