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Nine patients with untreated essential hypertension (random blood pressure 173/109 +/- 14/7 mmHg) were studied before and after 16 weeks' treatment with oral nifedipine 10 mg three times a day. Direct continuous measurement of the systolic and diastolic blood pressures showed that both values were significantly reduced during the 24 hour period. Nifedipine did not change the variability of the blood pressure. There was no significant change in the heart rate after treatment with nifedipine. Long-term nifedipine induced an increase in blood flow in the forearm and decreased the vascular resistances which confirmed the vasodilator effects of the drug. The absolute responses of the blood pressure during postural changes, the hand grip test and cold pressor test were reduced but the treatment did not change the percentage increase in blood pressure during these tests. Long-term nifedipine therapy did not affect the plasma renin activity. The sensitivity and characteristics of the baroreflex response to intravenous phenylephrine were measured. After long-term nifedipine therapy we observed a normalisation of the sino-aortic baroreflex and an increase in its sensitivity. Normalisation of the blood pressure by nifedipine induced a significant reduction in the index of left ventricular mass.