The effect of metabolic acidosis on the renin-aldosterone system remains unclear. In the present study anesthetized mongrel dogs (n = 19) were infused at similar rates with 0.45% NaCl (controls), HCl or NH<sub>4</sub>Cl (2.5mEq/kg) for 1-3 h. The induced metabolic acidosis in the two experimental groups was not associated with increases in plasma renin activity. Plasma cortisol (as a marker for ACTH secretion) and serum potassium concentration increased in both HCl- and NH<sub>4</sub>Cl-treated animals. Plasma aldosterone increased after 30 min in the HCl group and 60 min in the NH<sub>4</sub>C1 group and did not change in controls. These findings demonstrate that metabolic acidosis induced by HCl or NH<sub>4</sub>Cl is associated with increased aldosterone production without concomitant changes in plasma renin activity.