This is an exercise involving the integration of a case presentation of diuretic-induced hypokalemia with the physiology of K+ balance. Students are presented with a case presentation involving the development and correction of diuretic-induced hypokalemia. K+ homeostasis, including the distribution of K+ in the body and total body K+ balance, is summarized. The renal handling of K+, including the filtered load, reabsorption by proximal segments of the nephron, and secretion by distal segments of the nephron, is outlined. The mechanisms for the control of the secretion of K+ are discussed. Finally, an exercise involving integration of the case presentation with the physiology of K+ balance is presented. This exercise works well in an interactive session with students. The exercise has proved highly useful in the presentation and understanding of basic concepts involved in the physiology of K+ balance.