This article reviews the role of the kidneys in the regulation of acid-base balance. It is intended as a guide for those who teach this aspect of renal physiology to health professions students. An approach is described, which begins with an overview of acid-base balance and then proceeds to describe the details of renal H+ transport and the important role the production and excretion of NH 4 + plays in the ability of the kidneys to generate new HCO 3 -. In the overview, the role of the kidneys in acid-base balance is placed in context for the student by examining the impact of diet and cellular metabolism on acid-base balance. Also, the interactions between the kidneys and lungs to maintain extracellular HCO 3 - concentration within a narrow range are described. This is followed by a detailed look at the cellular mechanisms of H+ secretion along the nephron, how these mechanisms are regulated, and how they result in the reabsorption of the filtered load of HCO 3 -. Finally, the important role of NH 4 + production and excretion in the generation of new HCO 3 - is reviewed and highlighted.