The effect of subpressor and pressor doses of angiotensin II was studied in 14 normal subjects. Ten of these received an intravenous magnesium load. Both doses caused a diminution of urinary magnesium, calcium, and sodium excretion, with reduction of the renal plasma and urinary flow. The magnesium infusion caused an increase in magnesium and calcium excretion; the absolute magnesium reabsorption remained unchanged, even when pressor doses of angiotensin II were used. A maximum reabsorption capacity for magnesium is suggested. The decrease observed in the urinary excretion of sodium, calcium, and magnesium under angiotensin II infusion could be mediated by the hemodynamic effects of the drug. The mechanism by which hemodynamically induced changes alter the fractional electrolyte reabsorption is still unclear.