Metabolic alkalosis (MA) only occurs after bicarbonate administration if given quickly and massively, or in the presence of renal failure. Most cases of MA are caused by a loss of hydrogen ions. This paper reviews the common causes (gastric aspiration, chronic diuretic therapy) and updates the list of drugs which may lead to this complication. Rare causes (such as hyper mineralo-corticoid secretion) should be suspected in patients with MA unresponsive to usual doses of potassium chloride. Hydrochloric acid infusions are reserved for very special cases.