The efficacy of nifedipine (N) as a "step 3" antihypertensive drug was assessed in 15 patients who remained hypertensive in spite of atenolol 100 mg and bendrofluazide 5 mg daily. Nifedipine was added in doses of 10, 20, and 30 mg three times daily in a placebo-controlled double-blind trial. Supine mean blood pressure was reduced by 11.9% +/- 6.2% by N 10 mg three times daily, by 13.9% +/- 7.6% by N 20 mg three times daily and by 20.3% +/- 6.2% by N 30 mg three times daily. Plasma potassium was reduced from 3.9 +/- 0.5 mEq/liter on placebo to 3.6 +/- 0.5 mEq/liter on N 10 mg three times daily, 3.6 +/- 0.4 mEq/liter on N 20 mg three times daily (p less than 0.05), and 3.5 +/- 0.5 mEq/liter on N 30 mg three times daily (p less than 0.05). Heart rate, body weight, renal function, and plasma glucose were not altered. Nifedipine is thus a useful third-line hypotensive agent that should be used in combination with a potassium-sparing diuretic.