Basic FGF mRNA induction by bFGF was investigated in cell cultures from rat brain, i.e. postnatal day 2 cortex and embryonic day 18 hippocampus. In situ hybridization shows that after bFGF treatment (10(-10) M) for 14 h neurones and glial cells show a remarkable increase in bFGF mRNA production. Incubation of astrocytes with antisense bFGF phosphorothioate oligodeoxynucleotides (bFGF-PTOs) resulted in an inhibition of both bFGF induced and serum induced proliferation. The results indicate that bFGF is capable of inducing its own mRNA production. This induction, i.e. new synthesis of bFGF mRNA, seems to be essential for the mitogenic effect of both bFGF and serum components.