Severe water and electrolyte disturbances were observed in a patient after a bout of very heavy beer drinking (30 liters in 6 days). On admission she was found to have hypokalemia (2.2 mEq/I), metabolic alkalosis (pHa: 7.55-total CO2: 40 mEq/I), and more particularly hyponatremia (109 mEq/I), responsible for the typical neurological signs of water intoxication (hyponatremic encephalopathy). There was a positive cumulative return of sodium (570 mEq) and chloride (900 mEq) levels, and normal conditions were restored without significant modifications in water balance or weight. No other etiology, apart from the beer, was discovered. Heavy drinking of beer alone can therefore provoke chloride and sodium depletion, probably because beer, which is poor in NaCl, must produce urinary loss of these electrolytes. The high osmolarity of beer may explain this latter phenomenon. This particular cause of hyponatremia should be recognized, if only to avoid confusing the clinical signs of alcoholic intoxication with those due to water intoxication.