Metabolic alkalosis is a primary pathophysiologic event characterized by the gain of bicarbonate or the loss of nonvolatile acid from extracellular fluid. The kidney preserves normal acid-base balance by two mechanisms: bicarbonate reclamation, mainly in the proximal tubule, and bicarbonate generation, predominantly in the distal nephron. Bicarbonate reclamation is mediated mainly by a Na(+)-H(+) antiporter and to a smaller extent by the H(+)-ATPase (adenosine triphosphate-ase). The principal factors affecting HCO3(-) reabsorption include effective arterial blood volume, glomerular filtration rate, chloride, and potassium. Bicarbonate regeneration is primarily affected by distal Na(+) delivery and reabsorption, aldosterone, arterial pH, and arterial partial pressure of carbon dioxide. To generate metabolic alkalosis, either a gain of base or a loss of acid must occur. The loss of acid may be via the gastrointestinal tract or via the kidney. Excess base may be gained by oral or parenteral HCO3(-) administration or by lactate, acetate, or citrate administration. Factors that help maintain metabolic alkalosis include decreased glomerular filtration rate, volume contraction, hypokalemia, hypochloremia, and aldosterone excess. Clinical states associated with metabolic alkalosis are vomiting, mineralocorticoid excess, the adrenogenital syndrome, licorice ingestion, diuretic administration, and Bartter's and Gitelman's syndromes. The effects of metabolic alkalosis on the body are variable and include effects on the central nervous system, myocardium, skeletal muscle, and liver. Treatment of this disorder is simple, once the pathophysiology of the cause is delineated. Therapy consists of reversing the contributory factors that are promoting the alkalosis and, in severe cases, administration of carbonic anhydrase inhibitors, acid infusion, and low bicarbonate dialysis.