The maintenance of K+ balance is essential for a variety of cellular functions and in neuromuscular transmission. Regulation of the distribution of K+ is very efficient, in order to prevent fatal rise in extracellular potassium concentration. Two important physiologic factors that facilitate the disposition of an acute K+ load are epinephrine and insulin. These hormones do not regulate the baseline plasma K+ concentration. Potassium enters the body by dietary intake or IV infusion, is primarily stored in the cells, and is then excreted in the urine, and to a lesser extent, in the stool and in the sweat. An abnormality in any one or more of these processes can lead to hypokalemia. The etiology of hypokalemia can usually be identified from a detailed history. The most common causes of hypokalemia are vomiting, diarrhea, use of diuretics, or laxatives.