The long-range objective of this project is to prevent progression of diabetic nephropathy, the leading cause of end-stage renal disease (ESRD). In most patients diabetic nephropathy progresses inexorably to ESRD despite inhibition of the renin-angiotensin- aldosterone system with angiotensin converting enzyme inhibitors (ACEIs) or angiotensin II type 1 receptor blockers (ARBs). The specific aims of this proposal are to: 1) recruit a multiethnic cohort of 78 young adults (ages 20-40) with type 1 (n=36) or type 2 (n=36) diabetes and overt nephropathy (defined as a urine albumin/creatinine ratio > 300 mg albumin/g creatinine) and randomize in a double blind fashion to a control group consisting of ACEI-based therapy alone (ramipril 40 mg once daily) or one of two experimental groups: a) ACEI + ARB (ramipril 40 mg once daily plus losartan 100 mg once daily) or b) ACEI + mineralocorticoid receptor antagonist (MRA) (ramipril 40 mg once daily plus spironolactone 25 mg once daily); 2) conduct a 12-month prospective study to determine if proteinuria is reduced to a greater extent when either the ARB or MRA is added to ACEi-based therapy. This study is powered to detect a 30% greater reduction in 24-hour urine albumin/creatinine ratio in either experimental group versus control (alpha = 0.05, beta=0.10, repeated measures analysis of variance). Secondary endpoints to be examined include: (a) serum potassium and creatinine to assess safety, (b) TGF-beta, as a surrogate marker for ongoing renal injury, (c) plasma renin activity, angiotensin II and aldosterone levels and (d) plasma lipids and lipoprotein composition; and 3) perform repeated ambulatory blood pressure monitoring (ABPM) to examine the renoprotective effect of the 3 different regimens at comparable 24-hour BP of < 125/75 mmHg. The deliverables include: 1) documentation of the safety of maximal dose combination therapy; 2) the feasibility of utilizing 24-hr ABPM to establish BP independent renoprotective effects of specific antihypertensive therapies; and 3) provide preliminary data for future large-scale studies to test efficacy and safety of combining ACEi with MRA therapy on renal outcomes.