Despite improvements in the past 20 years in glycemic and blood pressure control and the introduction of 'renoprotective' drugs such as renin-angiotensin system blockers, the incidence of end-stage renal disease (ESRD) in type 1 diabetes (T1D) is not declining. Novel therapies to complement these interventions are urgently needed. Mounting evidence from prospective studies indicates that moderately elevated serum uric acid is a strong, independent predictor of an increased risk of chronic kidney disease and increased rates of loss of kidney function among T1D persons. To study whether uric acid lowering can reduce glomerular filtration rate (GFR) loss in T1D, we have established the PERL (Preventing Early Renal Function Loss in Diabetes) Consortium including investigators from Joslin Diabetes Center, the Universities of Minnesota, Colorado, Toronto, and Michigan, Northwestern University, Albert Einstein College of Medicine, and the Steno Diabetes Center in Denmark. With the support of NIH grant R03 DK094484, the Consortium has designed a three-year, multi-center, double-blind, placebo-controlled, randomized clinical trial with the specific aim of evaluating the efficacy of the urate-lowering drug allopurinol, as compared to placebo, in reducing kidney function loss among subjects with T1D. The trial is targeted to T1D patients with microalbuminuria or moderate macroalbuminuria or ongoing kidney function decline and serum uric acid levels ≥ 4.5 mg/dl, since these are the patients who are at very high risk of having rapid GFR decline and might benefit most from reductions in uric acid levels. Study subjects will be required to have a GFR between 40 and 99 ml/min/1.73 m2, consistent with the goal of intervening relatively early in the course of clinical DN rather than at later stages when structural changes are far advanced and a very large proportion of kidney function has already been lost. The primary endpoint of the study will be the GFR (as measured by iohexol plasma disappearance) at the end of a 2-month wash-out period after the 3-year intervention. Sample size calculations under various dropout and non-adherence scenarios suggest that 240 subjects in each treatment arm would provide at least 80% power to detect a clinically meaningful and achievable reduction in GFR decline in the allopurinol vs. the placebo group.If we demonstrate that allopurinol can halt or slow down GFR decline in T1D subjects, we will provide a safe and inexpensive intervention to prevent or delay kidney failure in T1D that can be applied at the earliest clinically detectable stages of renal injury. It is difficult to overstate how significant this finding would be, both from the perspective of public health and that of persons with diabetes.