Angiotensin converting enzyme inhibitors (ACE-Is) and angiotensin II receptor blockers (ARBs) are frequently used for the treatment for glomerulonephritis and diabetic nephropathy because of their albuminuria- or proteinuria-reducing effects. To many patients who are nonresponsive to monotherapy with these agents, combination therapy appears to be a good treatment option. In the present study, we examined the effects of the addition of an ARB (losartan) followed by titration upon addition and at 3 and 6 months (n=14) and the addition of an ACE-I followed by titration upon addition and at 3 and 6 months (n=20) to the drug regimen treatment protocol in type 2 diabetic patients with nephropathy for whom more than 3-month administration of an ACE-I or the combination of an ACE-I plus a conventional antihypertensive was ineffective to achieve a blood pressure (BP) of 130/80 mmHg and to reduce urinary albumin to <30 mg/day. During the 12-month treatment, addition of losartan or addition of an ACE-I to the treatment protocol reduced systolic blood pressure (SBP) by 10% and 12%, diastolic blood pressure (DBP) by 7% and 4%, and urinary albumin excretion by 38% and 20% of the baseline value, respectively. However, the effects on both BP and urinary albumin were not significantly different between the two therapies. In conclusion, addition of losartan or an ACE-I to an ongoing treatment with an ACE-I, or addition of an ACE-I to ongoing treatment with a conventional antihypertensive were equally effective at reducing the urinary albumin excretion and BP, and provided renal protection in patients with type-2 diabetic nephropathy.