Noradrenaline and noradrenaline turnover were determined in regions enriched in catecholamine nuclei of the brainstem (A1, A2, C1, C2 and C3), in the locus coeruleus (A6) and in the nucleus tractus spinalis n. trigemini (Sp5C) of Wistar Kyoto and spontaneously hypertensive rats at four ages from 6 to 40 weeks. Adrenaline levels were also determined but were only consistently detected in the C1 and C2 regions. There was an age-related decline in noradrenaline concentrations in both strains of rats in all brainstem catecholamine nuclei however noradrenaline turnover decreased only in the A2 and C3 regions and this may contribute to the progressive rise in blood pressure with age in spontaneously hypertensive and Wistar Kyoto rats. Adrenaline levels did not alter with age providing evidence of a functional disassociation between adrenaline and noradrenaline neuronal systems. There were several strain-related differences in noradrenaline and adrenaline concentrations in the regions studied, however noradrenaline turnover was reduced only in the A2 and C2 regions (nucleus tractus solitarius) of spontaneously hypertensive rats which is consistent with the sympathoinhibitory role of this nucleus in central blood pressure regulation.