The subject of hyperpotassemia has assumed considerable importance in recent years. An excess of potassium produces profound disturbances in the organism in general and the heart in particular. The condition can be diagnosed relatively simply by clinical means, including the electrocardiogram, and may be confirmed by chemical determination. Hyperpotassemia kills primarily as a result of its cardiac effect, and this can, in most cases, be reversed by the various methods to be described below. Early recognition and prompt institution of proper therapy are of primary importance. The presence of hyperpotassemia may be said in many instances to constitute an acute cardiac emergency. The causes of hyperpotassemia include those conditions which lead to an increase in the extracellular potassium which the patient is unable to handle, generally because of renal insufficiency. The increase in extracellular potassium may be the result of the following factors: (a) increased tissue destruction, anoxia, the crush