This perspective on genetic renal tubular transport disorders selectively reviews the pathophysiology of renal apical Na+ transport systems. These transporters play an essential role in the control of extracellular fluid volume and blood pressure. Significant advancements in the understanding of the role of these genes in Mendelian forms of extracellular volume homeostatic disorders have been achieved in the recent years. Of even greater importance will be the ongoing definition of the various factors that regulate the expression and activity of the Na+ transport systems. These regulatory pathways, and the responses to environmental factors such as dietary salt, stress, and so on, may determine the appearance, severity and complexity of the clinical phenotypes that result from genetic disorders of the renal apical Na+ transporters. Copyright © 2001 by W.B. Saunders Company.