The Cl⁻/anion exchanger pendrin (SLC26A4) is expressed on the apical side of renal non-type A intercalated cells. The abundance of pendrin is reduced during metabolic acidosis induced by oral NH₄Cl loading. More recently, it has been shown that pendrin expression is increased during conditions associated with decreased urinary Cl⁻ excretion and decreased upon Cl⁻ loading. Hence, it is unclear if pendrin regulation during NH₄Cl-induced acidosis is primarily due the Cl⁻ load or acidosis. Therefore, we treated mice to increase urinary acidification, induce metabolic acidosis, or provide an oral Cl⁻ load and examined the systemic acid-base status, urinary acidification, urinary Cl⁻ excretion, and pendrin abundance in the kidney. NaCl or NH₄Cl increased urinary Cl⁻ excretion, whereas (NH₄)₂SO₄, Na₂SO₄, and acetazolamide treatments decreased urinary Cl⁻ excretion. NH₄Cl, (NH₄)₂SO₄, and acetazolamide caused metabolic acidosis and stimulated urinary net acid excretion. Pendrin expression was reduced under NaCl, NH₄Cl, and (NH₄)₂SO₄ loading and increased with the other treatments. (NH₄)₂SO₄ and acetazolamide treatments reduced the relative number of pendrin-expressing cells in the collecting duct. In a second series, animals were kept for 1 and 2 wk on a low-protein (20%) diet or a high-protein (50%) diet. The high-protein diet slightly increased urinary Cl⁻ excretion and strongly stimulated net acid excretion but did not alter pendrin expression. Thus, pendrin expression is primarily correlated with urinary Cl⁻ excretion but not blood Cl⁻. However, metabolic acidosis caused by acetazolamide or (NH₄)₂SO₄ loading prevented the increase or even reduced pendrin expression despite low urinary Cl⁻ excretion, suggesting an independent regulation by acid-base status.