Background The relationship between long-term heavy lead exposure and chronic interstitial nephropathy is well recognized in the previous literatures. Several epidemiological studies have demonstrated a positive association between blood lead levels and the age related decreases of renal function in the general population and suggested that environmental low-level lead exposure may accelerate the progression of renal function in the healthy persons. In addition, previous our works suggest environmental lead exposure may correlate to progressive renal insufficiency and lead chelation therapy or repeated lead chelation may improve and slow the progressive renal insufficiency in non-diabetic patients with chronic renal diseases. However, Diabetes mellitus is increasing in prevalence worldwide and is currently estimated to affect more than 6.5 percent of the population of the United States. In addition, diabetes is the most common cause of end-stage renal disease in many countries, accounting for about 40 percent of cases. It is still unknown that the relationship between long-term environmental lead exposure and the progressive renal insufficiency in patients with type II diabetes and diabetic nephropathy. Methods Ninety patints with type II diabetes and diabetic nephropathy (serum creatinine levels between 1.5 mg per deciliter and 3.9 mg per deciliter) who have a normal body lead burden and no history of exposure to lead or other metals will be observed for 24 months. Then, about 50 subjects with high normal body lead burdens (at least 80 μg but less than 600 μg) will be randomly assigned to the study and control groups. For three months, the 25 patients in the study group will receive lead-chelation therapy with calcium disodium EDTA weekly until the body lead burden fallsl below 50 μg, and the 25 control group receive weekly placebo. During the ensuing 12 months, the renal function will be regularly followed up every 3 months and EDTA mobilization tests will be assessed every 6 months. If body lead burden of the study group patients increase more than 60μg, the chelation therapy will be performed again until their body burden are less than 60 μg. The primary end point is an increase in the serum creatinine level to 2 times the base-line value during the observation period. A secondary end point is the change in renal function during the follow up period.