Significant magnesium deficiency occurs in chronic alcoholism. The evidence depends on a number of related lines of evidence: hypomagnesemia, a number of clinical symptoms in common with patients with nonalcoholic causes of magnesium deficiency, induction of magnesium excretion by alcohol ingestion (167-260% of control values), positive magnesium balance on alcohol withdrawal (average 1.15 meq/kg), decreased exchangeable magnesium (28Mg, mean deficit 1.12 meq/kg), a mean deficit of 11.4 meq/kg of fat-free dry weight of muscle of alcoholic patients, and hypocalcemia responsive only to magnesium therapy. When alcohol is withdrawn, free fatty acids rise sharply and plasma magnesium falls. Respiratory alkalosis occurs abruptly also on alcohol withdrawal. The alkalosis and rise of free fatty acids with concomitant fall of magnesium produces an acute instability of the internal milieu and could result in acute symptoms. There also are a number of nutritional deficiencies which need to be cared for, but magnesium, thiamine, and other B vitamins need to be administered immediately. Potassium and phosphorus should be supplied when they are low.