Microalbuminuria predicts early mortality and renal disease in non-insulin-dependent diabetic patients. In insulin-dependent diabetic patients, angiotensin converting enzyme inhibition decreases microalbuminuria and retards the progression of renal disease. The aim of this study was to evaluate the effect of low dose ramipril on albumin excretion rate (AER) and blood pressure in non-insulin-dependent diabetic patients with persistent microalbuminuria (AER > 20 < 200 micrograms/min) and normal blood pressure or mild hypertension. The study was a randomized, double-blind, placebo-controlled clinical trial of 6 months duration at 14 hospital-based diabetes centers in northeastern Italy. Blood pressure, plasma glucose, and body weight were determined every month; AER, serum creatinine, glycosylated hemoglobin, and plasma lipids at baseline, after 1 month, and at the end of the study. Of 122 non-insulin-dependent diabetic patients randomly allocated in blocks of four to receive either ramipril (1.25 mg/day) or placebo, 108 (54 in the ramipril group and 54 in the placebo group) completed the study. At baseline, age, duration of diabetes, body mass index, and glycosylated hemoglobin were similar in the two groups and remained unchanged throughout the study. In the placebo group, AER rose from a baseline median of 65 micrograms/min (range 53 to 76, 95% confidence Interval) to 72 micrograms/min (57 to 87) and to 83 micrograms/min (62 to 104) after 1 and 6 months, respectively, but fell from 62 micrograms/min (48 to 76) to 45 micrograms/min (33 to 57) and to 53 micrograms/min (38 to 69), respectively, in the ramipril group, a significant difference between the groups (P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)