By means of two colour immunofluorescence procedures it has been possible to demonstrate in the rat brain the coexistence of TH and bFGF immunoreactivities (IRs) in the perikarya of large numbers of noradrenaline (NA) nerve cells of the locus coeruleus and of the NA cell groups A1, A5 and A7 and in many perikarya of the adrenaline (A) cell groups C1, C2 and C3. The coexistence of 5-hydroxytryptamine (5-HT) and bFGF IRs was demonstrated in the perikarya of large numbers of 5-HT nerve cells of practically all raphe nuclei. These results open up the possibility that bFGF may have a trophic role in the NA, A and 5-HT cell groups of the rat brain.