Previous study showed repeated lead chelation therapy significant reduced progressive renal insufficiency in patients with chronic renal diseases and high-normal body lead burden in a placebo-controlled, randomized, 2-year clinical trial, even factors that influence progression, such as blood pressure, the presence or absence of hyperlipidemia, and urinary protein excretion were well controlled.Since relative small sample size and short duration of follow-up were noted in the previous study, whether repeated lead chelation therapy could long-term retard the progression of renal insufficiency remains unknown. Hence, we conducted a 51-month placebo-controlled clinical trial to assess the long-term effect of repeated chelation in progressive renal insufficiency of patients with high-normal body lead burden.