To investigate the role of central catecholaminergic pathways in the development of hypertension in the spontaneously hypertensive rat (SHR) the effects of intracerebroventricular (i.c.v.) injections of 6-hydroxydopamine (6-OHDA) were compared with those of local injections near the main ascending noradrenergic pathways. The parameters studied were systolic blood pressure, heart rate and regional catecholamine concentrations in micropunched brain areas. I.c.v. treatment with 6-OHDA (three 200 micrograms injections) of young SHR attenuated the development of hypertension and caused widespread depletion of noradrenaline and to a lesser extent of dopamine and adrenaline. 6-OHDA-induced lesions of the dorsal and ventral noradrenergic bundles did not affect the rise in blood pressure but induced a depletion of forebrain noradrenaline comparable to that after the i.c.v. treatment. Dopamine and adrenaline levels were, however, not substantially affected. These results suggest that forebrain noradrenergic innervation may not be of major importance for the development of hypertension in the SHR.