This study aimed to investigate the relationship between microalbuminuria and office blood pressure (BP) as compared with ambulatory BP in patients with diabetes mellitus under everyday practice conditions. It was also undertaken to assess the effect of the angiotensin converting enzyme inhibitor cilazapril on diabetes-associated albuminuria. Ambulatory BP was recorded during daytime in 54 patients with type II diabetes mellitus at the end of a 4-week period during which they received no vasoactive drug. The difference between office and ambulatory BP was unpredictable in the individual patient. There was no significant correlation between either ambulatory or office BP and urinary albumin/p5eatinine ratio. Fifty-one patients underwent a 40-week treatment with 5 mg/day of cilazapril. There was, in the absence of satisfactory BP control, the possibility of adding the calcium antagonist amlodipine (5 mg/day) from the 10th week onward and 12.5 mg/day of hydrochlorothiazide from the 20th week onward. Office mean BP was significantly reduced after 30 to 40 weeks of therapy in patients with normoalbuminuria (n = 19, -14%, P < .001), in those with microalbuminuria (n = 22, -6.6%, P < .01), as well as in those with clinical proteinuria (n = 9, -11.4%, P < .01). During the same time, the urinary albumin/creatinine ratio was not modified in normoalbuminuric patients (n = 19, +24.6%, P = .72) as well as in those with clinical proteinuria (n = 9, -29.4%, P = .09). On the other hand this value was significantly reduced for the group with microalbuminuria (n = 23, -24.3%, P < .05). In the overall population, as well as in hyperalbuminuric patients (patients with microalbuminuria + patients with clinical proteinuria), the reduction of the albumin/ creatinine ratio was also significant (n = 51, -7%, P < .01 and n = 32, -25,7%, P < .01, respectively). In conclusion, the findings of this study performed by practicing physicians show that ambulatory BP may differ greatly from office BP in diabetic patients. They also indicate that urinary albumin excretion is poorly correlated with office and ambulatory BP in type II diabetics. Finally, they demonstrate the antiproteinuric action of prolonged treatment with the angiotensin converting enzyme inhibitor cilazapril, whether given alone or combined with amlodipine.