It has been reported that treatment with an angiotensin-converting enzyme (ACE) inhibitor is not adequate to suppress aldosterone, and we previously demonstrated that adding spironolactone to an ACE inhibitor may have beneficial effects on left ventricular hypertrophy (LVH) in selected patients with essential hypertension (EH). We have extended our previous short-term study, and addressed the relative long-term clinical effects of spironolactone and an ACE inhibitor in patients with EH who have LVH. Twenty patients with EH and concomitant LVH participated in this study. Subjects were treated with either an ACE inhibitor alone (group 1: 10 patients) or an ACE inhibitor plus spironolactone at the dose of 25 mg (group 2: 10 patients) for 60 weeks. The baseline clinical and echocardiographic characteristics of the two groups were similar. Final values of blood pressure were also similar between the two groups. The LV mass index (LVMI) decreased significantly in both groups, but the extent of reduction was significantly greater in group 2 at 60 weeks. The early peak to atrial peak filling velosities ratio (E/A ratio) was significantly increased to a similar extent in both groups. Serum procollagen type III amino-terminal peptide (PIIINP) was significantly decreased in group 2, but not in group 1. In group 2, there was a statistically significant correlation between the changes in LVMI and PIIINP. In conclusion, adding spironolactone to therapy with an ACE inhibitor for 60 weeks may have beneficial effects in patients with EH and concomitant LVH. Our study strongly suggests the possibility that attenuation of the effects of cardiac aldosterone in patients with EH by treatment with spironolactone and an ACE inhibitor may become a new goal for the prevention and regression of cardiac hypertrophy. (Hypertens Res 2002; 25: 837-842)