In the body fluids of patients suffering from acute mercury poisoning the changes in the concentration of electrolytes may be profound. Few other diseases are associated with a greater disturbance of acidbase equilibrium than is observed in this condition. Addison's disease, 1 diabetic coma 2 and heat cramps 3 are examples of morbid conditions which are associated with recovery as the disordered equilibrium is corrected. Advanced renal insufficiency, on the other hand, is a disease with electrolyte imbalance which resists restoration to normal and ends with a disintegration of the chemical structure of the body. 4 Acute mercury poisoning sometimes belongs in one category, sometimes in the other. In this communication there will be described the several changes in the concentration of electrolytes in a patient who recovered from acute and severe mercury poisoning. The amount of mercury bichloride which was ingested was believed to have been 1 Gm. Usually