Direct conscious blood pressure (BP) was measured via indwelling femoral cannula to evaluate the effects of chronic diet supplements with Na, Ca or both, offered to 3-week-old weanling spontaneously hypertensive rats (SHR). Despite similar food intakes, body weights were reduced within 1-2 weeks on high-Ca diets. Blood pressure was unchanged by 5.5 weeks of diet treatments. However, irrespective of concomitant Na supplement, more prolonged treatment with the high-Ca diet completely abolished the further increase in BP between the 9th and 12th weeks of age, which was noted in the rats fed the normal or high-Na diets. Angiotensin-stimulated BP was attenuated by high-Ca diets regardless of diet Na, similar to basal readings. These weight and pressure effects of Ca were not reproduced by high-Na diet alone. For all four groups, BP was directly and significantly correlated with body weight, both at 9 and 12 weeks of age. These studies demonstrate the potential role of growth retardation in the antihypertensive action of oral Ca loading in young rats.