The use of nisoldipine (10-20 mg b.i.d.) was evaluated as a replacement therapy for long-acting nifedipine (40-120 mg/day) in 21 patients with severe hypertension, who were resistant to or intolerant of nifedipine. Except for one patient with specific contraindications, all participants received an individually determined constant dose of beta blocker throughout the 8-month study. Results indicated a significant decrease in blood pressure after four weeks of treatment with nisoldipine (173 +/- 5/98 +/- 4 to 156 +/- 3/91 +/- 2 mmHg, p less than 0.05) without an associated change in pulse rate in 19 patients; only 5 of the 21 patients showed no further benefit from nisoldipine. No significant biochemical changes were noted in any of the patients during the study. In three patients, leg edema that had developed as a consequence of previous nifedipine therapy resolved completely following nisoldipine administration. Two patients withdrew from the study before term because of headaches and palpitations. An additional two patients suffered headaches, but tolerated the drug and continued the study. One patient suffered from polyuria. Nisoldipine appears to be an effective substitute treatment for nifedipine in severely hypertensive patients sensitive or resistant to nifedipine.