To assess the effect of potent vasodilator therapy in patients with severe or resistant hypertension, 10 patients underwent therapy with Captopril and nifedipine alone and in combination. Blood pressure (BP), heart rate, and blood chemistry values were monitored for 4 weeks during Captopril monotherapy and after 8 weeks during combination therapy with Captopril and nifedipine. Compared with baseline, the BP decreased during Captopril monotherapy (180 ± 11/98 ± 7 vs. 209 ± 16/118 ± 12 mm Hg; P<0.005). After the addition of nifedipine, the BP was further reduced (148 ± 23/85 ± 16 mm Hg), but there was no change in heart rate. In three patients not achieving the diastolic BP goal during combination therapy with dosing every 8 hours, automatic 24‐hour ambulatory BP monitoring demonstrated lack of antihypertensive control for only the last 2 to 3 hours of the dosing interval. These data demonstrate that combination therapy with Captopril and nifedipine is effective in patients with severe hypertension, but frequent dosing intervals are necessary for adequate antihypertensive control.Clinical Pharmacology and Therapeutics(1986)39,43–48; doi:10.1038/c