Calcium antagonists are increasingly used in the treatment of primary and secondary hypertension. A new substance of this group, isobutyl methyl 1,4-dihydro-2,6-dimethyl-4-(2-nitrophenyl)-3,5-pyridinecarboxylate (nisoldipine, Bay k 5552) inhibits the calcium-induced contraction of arteries and veins in concentrations 5-20 times lower compared to those of nifedipine in vitro. The effect of nisoldipine (10 mg orally) on blood pressure and heart rate in supine and upright position, on serum electrolytes (Na+, K+, Ca2+) and on serum aldosterone and serum hydrocortisone (cortisol) was comparatively studied in patients with essential hypertension (n = 6, 57 +/- 7 years), in patients with hypertension and chronic renal failure (n = 6, 46 +/- 4 years, serum creatinine 2.1 +/- 0.5 mg/100 ml) and in 6 patients with unilateral renal artery stenosis. In patients with essential hypertension, systolic blood pressure (BP) dropped by 26 mmHg; diastolic BP was lowered by 17 mmHg after 150 min compared to placebo. In patients with chronic renal failure, decrement in BP was 25/16 mmHg (systolic and diastolic BP, respectively). In patients with renal artery stenosis, blood pressure declined by 31/18 mmHg after nisoldipine. Serum electrolytes (Na+, K+ and Ca2+) and serum aldosterone as well as serum hydrocortisone remained unchanged. The hypotensive action of nisoldipine seems to be independent of the type of hypertension. However, the hypotensive activity correlates with the level of the baseline blood pressure.