In order to assess the effective dose, tolerability, and safety of isradipine as a monotherapeutic antihypertensive agent for Chinese patients in Taiwan, an open trial was carried out. This study consisted of a 2-week, placebo, run-in period and an 8-week active treatment period, starting with isradipine 1.25 mg twice daily (bid) for the first 4 weeks, followed by 2.5 mg bid if the blood pressure was not normalized (diastole < 90 mmHg). One hundred and one patients (M/F = 48:53) were valid for efficacy analysis. Their age ranged from 30 to 64 years (mean +/- SD, 52 +/- 8). The blood pressure before active treatment was 160 +/- 2/104 +/- 1 mmHg. At the end of treatment period I (week 4), 12-14 hours after the last dose, 38 (37.6%) patients were normalized and 47 (46.5%) subjects responded (diastolic blood pressure reduction > or = 10 mmHg). At week 8, 68 (67.3%) patients were normalized and 79 (78.2%) subjects responded. Isradipine reduced both systolic and diastolic blood pressures within 2 weeks of treatment. There were no significant differences in blood pressure reduction between both genders and among age groups. Safety analysis showed two subjects with severe flushing, dizziness, and palpitation who used the dose of 1.25 mg bid. They withdrew from the study. The adverse reactions of other patients were transient, mild, and tolerable. Most of the side effects were related to vasodilatation, but edema was not found. There was no change in body weight or heart rate, nor any atrioventricular conduction disturbances.(ABSTRACT TRUNCATED AT 250 WORDS)