A certain percentage of aldosterone (ALD) breakthrough generally occurs in patients with hypertension and chronic heart failure and is an important issue during long-term treatment with angiotensin-converting enzyme inhibitors (ACE-I) and angiotensin receptor blockers (ARB). It has been reported that efonidipine decreases the plasma levels of ALD. However, the long-term effects of efonidipine on the plasma levels of ALD and the left ventricular mass index (LVMI) remain unknown in patients with hypertension. Sixty stable outpatients with essential hypertension who had received amlodipine and ACE-I or ARB for more than 1 year were randomized into two groups (amlodipine group (n=30): continuous amlodipine treatment at a stable dose; efonidipine group (n=30): amlodipine (5 mg day(-1)) was changed to efonidipine at a dose of 40 mg day(-1)). There was no difference in their baseline characteristics including the LVMI and plasma levels of ALD. In the amlodipine group, there were no significant changes in blood pressure, LVMI or plasma levels of ALD for 18 months. In the efonidipine group, blood pressure did not change after replacement of amlodipine with efonidipine, although there was a significant decrease in the plasma levels of ALD after 6 months. The decrease in ALD was sustained for 18 months and LVMI was significantly decreased after 18 months (121+/-25 vs. 114+/-21 g m(-2), P<0.05). There was a significant correlation between the changes in LVMI and % changes of ALD in the efonidipine group. These findings indicate that the effect of efonidipine on the suppression of plasma ALD was sustained for at least 18 months and that long-term efonidipine therapy decreases LVMI in patients with essential hypertension.