The efficacy and safety of amlodipine in the long term treatment of outpatients with mild to moderate hypertension were examined in an open, non-comparative study. 87 patients were enrolled in the study, 62 (71%) of whom were observed for 27 months under controlled conditions. Daily doses of 5-10 mg amlodipine led to a statistically significant decrease in systolic and diastolic blood pressure (-30.5/-20.7 mmHg, p less than 0.01) while there was no substantial influence on heart rate or decrease in efficacy. Amlodipine was tolerated very well; only 17% of the patients reported side effects, most of which were either mild or moderate and were tolerated or disappeared with continued treatment. No clinically significant changes were noted in clinical laboratory or ECG examinations. Based on its special pharmacological and pharmacokinetic properties, amlodipine is a novel calcium antagonist from the dihydropyridine class which has proved to be effective in the treatment of hypertension. The antihypertensive effect, which is sustained for more than 24 hours, parallels the circadian variations in blood pressure and thus induces beneficial pharmacodynamic effects. Due to the low incidence of side effects and the once-daily dosage regimen, an improvement in patient compliance can be expected.