Fifty consecutive black patients with very severe hypertension (sitting diastolic blood pressure > or = 120 mm Hg and systolic > or = 210 mm Hg by the conventional cuff method) were treated in an open-label study (without a placebo or active drug control group) for 3 months with a long-acting preparation of isradipine (Dynacirc SRO), during which time serial changes in 24-h ambulatory blood pressure monitoring (ABPM), left ventricular (LV) mass index, and LV systolic function were evaluated. Mean 24-h ABPM was reduced from 184 +/- 13/119 +/- 6 to 148 +/- 18/96 +/- 11 mm Hg at 3 months (P < .0001). The reduction in BP was sustained for 24 h after dosing. Simultaneous BP measurements using a conventional cuff method and Dinamap were significantly different from the ABPM pre- and posttherapy, suggesting a marked "white coat" pressor effect. LV mass index regressed from 143 +/- 36 to 122 +/- 32 g/m2 at 3 months (P < .02). Heart rate and mean body weight were unchanged. Left ventricular performance was not adversely affected. Cardiac index and fractional shortening changed insignificantly, from 2.6 +/- 0.6 to 2.7 +/- 0.5 L/min/m2, and from 28 +/- 6 to 31 +/- 7%, respectively. Adverse effects were few and tended to disappear during the treatment period. All of the clinical laboratory parameters tested remained unchanged. We conclude that in this group of patients long-acting isradipine 1) showed a marked and sustained antihypertensive action demonstrated by 24-h ABPM; and 2) was well tolerated and associated with LV mass regression without adverse effect on systolic cardiac function.(ABSTRACT TRUNCATED AT 250 WORDS)