A 6-week open study of the introduction of isradipine treatment was conducted in general practice in Hong Kong. 303 Chinese patients with mild to moderate hypertension entered the study. Side effects were reported in 21% of patients and caused withdrawal from the study in 3 patients. The main side-effects were headache, dizziness, palpitation and flushing and these were not more frequent than reported in other studies with isradipine or with placebo. Supine blood pressure was reduced (P less than 0.01) from 170 +/- 20/102 +/- 6 mmHg to 153 +/- 19/92 +/- 8, 147 +/- 18/88 +/- 7 and 144 +/- 14/87 +/- 6 mmHg at 2, 4 and 6 weeks respectively in evaluable patients. Similar reductions occurred in standing blood pressure and there was no evidence of postural hypotension. Normalization and responder rates at 6 weeks were 86% and 69% respectively. Dosage was increased from 2.5 mg b.d. to 5 mg b.d. at 4 weeks in patients with diastolic blood pressure greater than 90 mmHg and their further response was greater than those remaining on 2.5 mg b.d.