The efficacy of the calcium channel blocker nitrendipine alone and in combination with the beta blocking agent acebutolol or hydrochlorothiazide was tested in 34 patients with moderate essential hypertension. After a wash out period of three to four weeks, all patients received placebo for two weeks, thereafter 20 mg of nitrendipine per day for four weeks. When diastolic blood pressure remained above 95 mmHg with nitrendipine, acebutolol (200 mg/d) or the thiazide (25 mg/d) was added in a randomised double-blind fashion. With nitrendipine alone, blood pressure could be normalized in nine patients with a drop in pressure from 168/108 to 152/89 mmHg. The other patients showed a fall in blood pressure from 164/110 to 152/102 mmHg. In these patients, the addition of acebutolol or thiazide was followed by a further fall in blood pressure which was similar with both drugs. With acebutolol blood pressure decreased from 154/102 to 146/94 mmHg and with the thiazide from 152/102 to 147/95 mmHg, respectively. Minor and mostly transient side effects were predominantly seen during therapy with nitrendipine alone. The fall in diastolic but not systolic blood pressure with nitrendipine was correlated with age. The blood pressure lowering effect of nitrendipine was independent of plasma renin activity and intracellular electrolyte concentrations. In the therapy of moderate hypertension, nitrendipine given in combination with a betablocker or a thiazide diuretic is effective and well tolerated.