SummaryAldosterone, discovered thirty years ago, has rapidly gained an enviable status among clinicians as well as biologists because of its key role as regulator of extra-cellular fluid volume—essentially through stimulation of sodium reabsorption in the distal parts of the nephron. This process has been fruitfully studied by taking advantage of amphibian epithelia carrying out transcellular sodium transport and resembling in this respect the distal renal tubule.Recent results suggest that, at least after prolonged incubation, not only is sodium entry (at the apical border) facilitated by aldosterone, but the latter steroid also somehow improves the handling of the ion by the«pump»located at the basal-lateral border. As a consequence, the target cells exposed to aldosterone are optimally geared for enhanced transcellular sodium transport.Biochemically, both of these aldosteronestimulated steps depend on what is nowadays considered the standard pattern of steroid hormone action: after interaction of aldosterone with protein receptors) present in the cytoplasm of target cells, and migration of the resulting complex to their nu cleus, synthesis of specific messenger ribonucleic acid is stimulated which leads to increased synthe sis of proteins eventually responsible for the physiological response.The biophysical and biochemical studies aimed at elucidating the mechanism of action of aldosterone continue to draw, heavily from therapeutic drugs such as spironolactone and amiloride. This illustrates anew how useful it is to link ever more tightly clinical Medicine and«basic»medical Sciences.