A total of 203 patients with hypertension (supine diastolic blood pressure of 100-119 mm Hg) from six centers entered into a 3-week placebo baseline followed by 5 weeks of active treatment (either placebo or isradipine 2.5, 5, 7.5, or 10 mg BID) to determine the effectiveness of isradipine on blood pressure control. Electrocardiographic criteria for left-ventricular ischemia were coded blindly using the Minnesota Codes 4-1 to 4-4 and 5-1 to 5-3 at the end of baseline and active treatment periods. One hundred seventy patients with hypertension and matching and complete electrocardiograms completed the study for analysis: 63 (37%) were white and 117 (69%) were men. They were 52.1 +/- 10.3 years old mean +/- SD; range: 22-77 years). No myocardial infarction occurred during the active phase. Fifty-eight of 170 (34%) at baseline and 54 of 116 (32%) at week 5 had left atrial enlargement. Romhilt-Estes left-ventricular hypertrophy was not significantly different at baseline versus active treatment: 14 of 170 (8.2%) versus 15 of 170 (8.8%). At baseline, the rate of active ischemia was 28.2% (48/170): 27.8% (10/36) were randomized to receive placebo during active treatment and 28.4% (38/134) were given isradipine (P = NS). For those without ischemia at baseline, the rate of change to electrocardiographic ischemia during active treatment was 0% (0/26) for those receiving placebo and 3.1% (3/96) for those taking isradipine (P = NS). For those with ischemia at baseline, the rate of change to no ischemia during active treatment was 20% (2/10) for those receiving placebo and 10.5% (4/38) for those taking isradipine (P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)