Felodipine (Plendil) is a once daily antihypertensive calcium antagonist. The present study evaluated the clinical efficacy and tolerability of felodipine as monotherapy in treating Asian patients with mild to moderate hypertension. Twenty-three males and 14 females with supine diastolic blood pressure (sDBP) above 95 mmHg after a 2-4 week placebo treatment period were included in the study. Active treatment was initiated with felodipine 10 mg once every morning for 2 weeks. The dose was titrated stepwise with increments of 10 mg every two weeks if BP was greater than the target DBP of 90 mmHg. The optimum dose was then maintained for at least 4 months during which the patients returned for 2 weekly follow-up visits. At each visit, supine and standing blood pressure and heart rate (HR) were measured after dosing. Any adverse events were recorded when they occurred. Blood chemistry was checked before and at 4 weeks after starting felodipine treatment and at the end of the study. The target DBP was achieved in all 37 patients, 25 with 10 mg, 11 with 20 mg and 1 with 30 mg. The supine BP was reduced to 127 +/- 10/83 +/- 5 by felodipine which was significantly lower than the pre-treatment BP (151 +/- 16/103 +/- 8, p less than .001). The BP control was maintained at the end of the study period (124 +/- 12/82 +/- 6). No significant changes in heart rates were detected after felodipine treatment. Side effects attributable to vasodilation were observed in 10 patients (transient headache in 8 and mild ankle oedema in 2), none requiring withdrawal of the drug. We conclude that felodipine 10-20 mg given once daily is an effective and well-tolerated monotherapy for the treatment of mild to moderate hypertension.