As direct vasodilating agents, calcium antagonists cause a significant reduction in total peripheral resistance in hypertensive patients. However, calcium antagonists differ significantly from direct vasodilating agents in their effects on sodium and water balance. Whereas direct vasodilating agents often cause sodium and water retention and the development of "pseudotolerance," calcium antagonists have no effect or cause a short-lasting natriuretic and diuretic effect. In our experience, dihydropyridine calcium antagonists with short-lasting and rapid onset of antihypertensive effect cause a significant rise in sodium and water excretion during the first and second days of oral administration. In contrast, calcium antagonists with a slower and longer-lasting blood pressure reduction cause a nonsignificant trend in sodium and water excretion with no signs or symptoms of retention. Finally, the antihypertensive effect of nifedipine is present in sodium-depleted and sodium-repleted patients. Calcium antagonists can increase sodium and water retention, although the antihypertensive effect is unrelated to their diuretic and natriuretic actions.