A number of acid-base or electrolyte disorders are associated with decreased or increased HCO3- reabsorption in the renal tubules. The present study was to examine the alterations of expression and distribution of Carbonic anhydrase II in the kidneys of normal and potassium-depleted rats using Western blot analysis and immuno-histochemistry. Western blot analysis demonstrated that CA II protein, ~30 kDa at molecular mass, was abundantly expressed in normal group. All potassium-depleted groups showed slightly increased CA II protein compared to normal group. In control group, immunoreactivity of CA II protein was detected in the entire collecting duct. Signal intensity was prominent in the intercalated cells and weak in the principal cells of the cortical collecting ducts. In potassium-depleted groups, the pattern of cellular labeling of CA II protein was identical to that of normal group, but the signal intensity was decreased in cortical collecting duct, markedly increased in the inner stripe of outer medullary and inner medullary collecting ducts, and unchanged in the outer stripe of outer medullary collecting duct. These results suggest that chronic hypokalemia impact the expression pattern of CA II protein depending the portion of the collecting duct.