The long-term haemodynamic responses to amlodipine, a new long-acting calcium antagonist, were studied both at rest and during exercise in 18 patients (mean age 43 years) with essential hypertension. Blood pressure was measured intra-arterially, cardiac output by dye dilution and heart rate by electrocardiogram. After 11 months of treatment with 5-10 mg amlodipine once daily (mean dose 9 mg/day), mean arterial pressure was reduced by 14% sitting at rest. The reduction in blood pressure was associated with a marked reduction in the total peripheral resistance index (TPRI) of 19% (P less than 0.001). Similar responses were seen supine at rest and during 50W, 100W and 150W bicycle exercise. No significant changes were seen in heart rate. There was a slight increase in stroke index, and cardiac index was preserved at rest and during exercise with a slight trend towards an increase. In 10 of the patients, blood pressure was monitored by a portable blood pressure recorder (Accutracker II, Suntech Medical instruments, Raleigh, North Carolina, USA). Blood pressure was well controlled throughout the full 24 h period after one daily dose. In conclusion, amlodipine exerts a clear antihypertensive effect, both at rest and during exercise, through reduction in the TPRI and without a fall in cardiac pump function. No changes in heart rate were seen and there was no tendency for a reduction in the stroke index during 8 min of exercise at 150 W; on the contrary there was a trend towards an increase. The incidence of side-effects was low (ankle oedema in two patients).