The sodium chloride cotransporter is regulated by the with-no-lysine kinases 1 and 4. Mutations in these genes are responsible for Mendelian hypertension, increased sodium chloride cotransporter activity, metabolic acidosis, and hyperkalemia. Explaining metabolic acidosis and hyperkalemia has been difficult. We now learn that the versatile bicarbonate-chloride exchanger, pendrin, is important in the process. As a result, we are confronted with still another mechanism causing renal tubular acidosis.