Amlodipine, a dihydropyridine calcium channel blocker (CCB), with a long duration of action, has been the subject of numerous controlled studies which showed its effectiveness and good tolerance in arterial hypertension in once-daily doses. We report the results of a large, multicentric, French, prospective phase IV study which evaluated the effectiveness and tolerance of amlodipine administered at a rate of 5 to 10 mg in only one daily dose. We also assess the evolution of the quality of life after 12 weeks of treatment among 31,946 hypertensive patients followed up to the ambulatory stage by general practitioners. The response rate--defined as the patients having had a reduction of 10 mmHg or more diastolic blood pressure--was 88%. The blood pressure standardization--defined by a diastolic blood pressure lower than 90 mmHg--was achieved for 70% of the patients. Amlodipine was administered in stand-alone therapy in 78% of the cases. The occurrence of an undesirable event was noted in the course of treatment in 12% of the patients and justified interruption of the treatment for 3.7% of the total population. The index average of quality of life was improved by the end of the 12-week treatment. This study carried out on a significant number of hypertensive patients (n = 31,946) under real prescription conditions confirms the efficacy and good tolerance of amlodipine, as has already been demonstrated in the preliminary developmental studies.