The efficacy of felodipine and tolerance of this drug was examined in 52 patients, 23 men and 29 women, 18-76 years of age, in whom it either replaced previous therapies of nifedipine and other vasodilators, or was added to a constant dose of beta blockers and diuretics or another previous therapy, which was unchanged. Felodipine significantly reduced blood pressure (BP), from 192.3 +/- 31.9/114.3 +/- 18.0 to 155.7 +/- 19.5/93.8 +/- 11.5 mm Hg, with no change in pulse rate. There were no significant biochemical changes, renal deterioration or blood sugar disequilibrium. Adverse reactions including flushes and leg edema could be tolerated by most of the patients, however six patients dropped out. Orthostasis dictated a decrease in felodipine dosage. Felodipine appears to be a highly potent, well tolerated drug and offers a substitute treatment for severe hypertensives refractory to other vasodilators.