Haemodynamic responses at rest and during exercise were studied in 18 patients with essential hypertension following long-term treatment with amlodipine. Patients underwent a 2-week placebo run-in period followed by a mean duration of 11 months' treatment with amlodipine 5-10 mg (mean dose 9 mg) once daily. Blood pressure was measured intra-arterially, cardiac output by dye dilution and heart rate by electrocardiogram. Amlodipine produced a mean reduction in systolic and diastolic arterial pressure of 27 and 16 mm Hg, respectively, at rest and after exercise. At rest sitting, mean systolic and diastolic arterial pressures were reduced by 16 and 14% (p less than 0.01), respectively, from initial mean values of 182.4/111.2 mm Hg. This reduction in blood pressure was associated with a marked reduction in the total peripheral resistance index of 19% (p less than 0.001). Similar responses were observed at rest supine and during exercise. No significant changes were seen in heart rate. Stroke index showed a small increase at rest and during exercise together with a trend towards an increase in cardiac index after treatment with amlodipine. Ambulatory blood pressure monitoring was carried out in 10 patients after the placebo run-in and at the end of the study. Amlodipine showed effective blood pressure control throughout the 24 h after one daily dose. The incidence of side effects was low (ankle oedema in 2 patients).