Calcium antagonists differ from traditional vasodilators by increasing renal water and sodium excretion, although the various calcium antagonist compounds influence renal excretory functions to a different extent. Two important aspects of the renal response to calcium antagonists are discussed, as they still need clarification: (a) the mechanisms of the diuretic and natriuretic effect; (b) the duration of this effect. Various mechanisms and sites of action can be envisaged to account for the diuretic and natriuretic action of these compounds. The action may be due to (a) a change in glomerular filtration rate and/or renal blood flow; (b) interference with renin release; (c) interference with aldosterone secretion and/or aldosterone action on distal tubule; (d) interference with adrenergic sodium handling; (e) a direct tubular action. Although the mechanisms may be multiple, the last type of action is likely to be the most important one. Recent balance studies of our group show that, although the diuretic and natriuretic actions of calcium antagonists are displayed acutely on the first or second day of administration, a negative sodium balance is maintained for at least 1 week, and the diuretic and natriuretic effects of these compounds are not overcome by water- and sodium-retaining mechanisms, unless the doses given are too large.