The effectiveness of nifedipine for the treatment of acute hypertensive episodes in patients already taking chronic calcium-channel blocker therapy is unknown. We report our experience with 43 consecutive patients who received nifedipine for acute hypertensive episodes in the coronary care unit. Of the 43 patients (24 men, 19 women), 23 (53 percent) were taking chronic (greater than 2 mo) calcium-channel blocker therapy. Nifedipine 10 mg capsules were chewed and swallowed with repeat doses given at hourly intervals if necessary. Target BP was 140/90 mm Hg, which was achieved in 31 of 43 patients (72 percent). In patients already taking calcium-channel blockers, target BP was achieved in 18 of 23 patients (78 percent). Response in patients not taking chronic calcium-channel blockers was observed in 13 of 20 patients (65 percent). Overall, adverse effects occurred in 16 of 43 patients (37 percent): 11 of 23 patients (48 percent) taking calcium-channel blockers, and 5 of 20 patients (25 percent) not taking calcium-channel blockers. Nifedipine is equally effective in lowering BP in patients taking calcium-channel blockers as it is in patients not taking them. Although associated with a higher incidence of adverse effects in patients already taking calcium-channel blockers, these effects were not considered serious. Nifedipine is an effective agent in acute hypertensive episodes, even in patients receiving chronic calcium-channel blocker therapy.