Spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were started at birth on sodium diets ranging from severely deficient (9 µmol) to a regular intake (101 µmol Na+/g food). Blood pressure and sympathetic activity were assessed at 6 and 16 weeks of age. At either age, SHR on 9 µmol Na+failed to develop hypertension. Spontaneously hypertensive rats on 17µmol Na+ exhibited significant blunting of the hypertension; SHR on 26 µmol showed a small amelioration. At 6 weeks, basal plasma noradrenaline was similar in SHR and WKY on 9 and 101 µmol Na+, whereas plasma adrenaline was increased in SHR at the lowest sodium level. At 16 weeks, both catecholamines were significantly increased in SHR on the 9 and 17 µmol sodium diet versus SHR on the control diet. Blood pressure responsiveness to noradrenaline was significantly decreased on 9 µmol Na+, but to a similar extent in both strains. In contrast, the blood pressure lowering effect of ganglionic blockade was markedly blunted in SHR on 9 µmol Na+and to a lesser extent on 17µmol Na+(both for percentage and absolute decrease) and 26 µmol Na+(only for absolute fall); however, this did not occur in WKY over the diet-range used.We conclude that a sodium-deficient diet from birth prevents/blunts the development of hypertension in SHR, at least partly by decreasing the pressor effect of the sympathetic nervous system