This study was performed to investigate the effects of different dietary magnesium levels on systolic blood pressure and mineral distribution in normotensive and spontaneously hypertensive rats. In experiment 1, Normotensive rats(NTR ; Sprague Dawley, Female) were given diets containing regular magnesium (0.05% Mg ; rMg), marginal magnesium (0.01% Mg ; mMg) or marginal magnesium with stress(0.01% Mg + stress ; mMg + Str). In experiment 2, spontaneously hypertensive rats (SHR ; Kyoto Wistar, Femal) were fed diets containing regular magnesium(0.05% Mg ; rMg) and high magnesium (0.2% Mg ; hMG). The following were found ; 1) NTR treated with marginal magnesium with stress showed significant increase in systolic blood pressure (SBP). Marginal magnesium diet without stress resulted in nonsignificant increase in SBP. Significant in crease of blood pressure showed in NTR treated with marginal magnesium and stress was associated with decreased magnesium and increased calcium content in femur, reticulocyte and plasma. 2) In experiment 2, magnesium supplementation to SHR showed significant attenuation of their systolic blood pressure with increasing age. The attenuation of SBP showed in SHR was associated with increased magnesium, lowered calcium content in cardiac muscle and reticulocyte and decreased plasma sodium and aldosterone level.