This study was designed to investigate the effect of delapril, an ACE inhibitor, and manidipine, a long action calcium antagonist, on persistent microalbuminuria in normotensive type 2 diabetic patients. Sixty type 2 diabetic patients were randomized to take delapril 30 mg/day or manidipine 10 mg/day for 48 weeks, in an open label design. Twenty eight of thirty subjects in the delapril group and twenty nine of thirty in the manidipine group completed the study. Urine albumin excretion as measured by the urinary albumin creatinine ratio decreased significantly in both groups (112.0+/-60.9 to 95.3+/-64.9 mg/g and 108.5+/-51.0 to 96.4+/-53.5 mg/g in the delapril and manidipine group respectively, p < 0.05, by paired t-test). Systolic and diastolic blood pressure were not significantly changed after treatment in the delapril group but significantly decreased in the manidipine group (130.9+/-7.1/80.2+/-6.1 to 127.2+/-7.1/78.0+/-5.3 mm/Hg, p < 0.05, by student's paired t-test). After 48 weeks of treatment, two patients in the delapril group and one patient in the manidipine group converted to normoalbuminuria (urinary albumin:creatinine ratio < 30 mg/g) and one patient in each group progressed to overt nephropathy (urinary albumin:creatinine ratio>> 300 mg/g). There were no significant changes in fasting plasma glucose, HbA1c, serum fructosamine, creatinine, potassium and lipid profiles after 48 weeks of treatment in both groups. Two cases in the delapril group were withdrawn during the study because of an intolerable cough and one case in the manidipine group because of intolerable dizziness and headache. In conclusion, both delapril and manidipine are effective in the reduction of microalbuminuria in normotensive type 2 diabetic patients with persistent microalbuminuria.