In order to investigate the efficacy of isradipine in the treatment of hypertensive crisis, we treated three groups of patients who had diastolic blood pressure (DBP) greater than 120 mm Hg, and who were without signs of acute target-organ damage. Isradipine was given sublingually in doses of 1.25 mg (group 1; n = 10), 2.5 mg (group 2; n = 10), and 5 mg (group 3; n = 7). Mean arterial pressure (MAP) was reduced in all patients [from 153.4 +/- 4.3 to 124.0 +/- 2.3 mm Hg at 60 min, and to 118.0 +/- 2.1 mm Hg at 2 h after administration (p less than 0.001)]. The heart rate (HR) did not change significantly (from 82.4 +/- 3.7 to 84.0 +/- 6 beats/min; NS). No significant differences were noted in the overall responses of the three groups; however, blood pressure reduction was more rapid in the group receiving 5 mg compared with the other two dosages. These results show that isradipine given sublingually is effective in reducing the elevated blood pressure of a hypertensive crisis and is not accompanied by limiting side effects. Isradipine's onset of action is early (approximately 30 min after dosing) and reaches its maximum blood pressure response within 2 h of administration. No dose-dependent reductions in blood pressure were observed with the dosage range employed in this study.