Thirty patients with mild to moderate essential hypertension entered a randomised double-blind parallel group study for 6 months to compare the effects of the new calcium channel blocker nicardipine 90 mg/day and propranolol 240 mg/day. Both drugs reduced systolic and diastolic blood pressures significantly in the supine and in standing positions. After 6 months of treatment, nicardipine had reduced the supine systolic and diastolic blood pressures by 16 and 17 mm Hg, respectively, and propranolol by 15 and 12 mm Hg. While propranolol treatment led to a marked decline in heart rate, nicardipine caused a small but statistically significant increase in heart rate throughout the study. Both drugs reduced blood pressure during maximal exercise, but propranolol had a greater effect. During exercise nicardipine did not affect the heart rate, whereas propranolol dramatically reduced it. Nicardipine did not produce any ECG changes at rest or during exercise. The side-effects for nicardipine were mild and were related to the vasodilatation induced by the drug. No abnormalities in routine blood chemical tests were found for either of the drugs. Nicardipine appears to be an effective single drug treatment for mild to moderate hypertension.