The effect of nisoldipine, a new calcium antagonist, on rats with renovascular hypertension was evaluated. Eight one-kidney, one clip hypertensive rats (1K, 1C rats) given nisoldipine 10 mg/kg for 4 weeks were compared with eight 1K, 1C hypertensive control rats. Fifteen other rats underwent sham-operation (right nephrectomy, no clip), of which eight received nisoldipine in the same dosage. A significant decrease in systolic blood pressure (BP) was achieved in the nisoldipine groups: from 154 +/- 4 to 107 +/- 7.5 mmHg in the 1K, 1C group (P less than 0.005) and from 117 +/- 4.2 to 89 +/- 5.4 mmHg in the sham-operated rats (P less than 0.01). The significant decrease in BP was maintained for only 6 days, but did not rise markedly throughout the entire study. Four 1K, 1C control rats died before term, two after 14 days and two after 20 days. There was no significant change in the pulse rate. Sugar and cholesterol levels in the nisoldipine groups remained constant. Nisoldipine caused a natriuresis without kaluresis in both groups: sodium excretion in the 1K, 1C rats increased from 0.25 +/- 0.05 to 2.32 +/- 0.2 mmol/day, and from 0.34 +/- 0.1 to 1.85 +/- 0.15 mmol/day in the sham-operated rats. A slight decrease in aldosterone levels in the 1K, 1C rats was observed. It appears that the combination of both natriuretic and vasodilatory effects during nisoldipine treatment results in a favourable hypotensive response in 1K, 1C hypertensive rats.