SummaryExploration of uremic acidosis in patients with severe CRF (creatinine clearance<20 ml/min) by means oi an crat NH CI loading test in combination with an IV HCO-3loading test, reveals the existence of three subtypes of acidosis.One particular type, characterized by tubular acidification disturbances and persistent bicarbonaturia in severe metabolic acidosis, is frequently seen in chronic interstitial nephritis. The acidification disturbance is probably related to the frequently associated salt wasting state of these patients. Since salt wasting in interstitial renal diseases can be prevented by gradual adaptation of the dietary salt intake, this therapy could also be useful to treat the associated, sometimes severe, acidosis.