One thousand patients with LHD who have no history of exposure to lead will be observed for 18 months. Blood lead level(BLL), biochemical data, hemoglobin, albumin, Cr, high sensitivity C-reactive protein (HsCRP), and blood cell counts are assessed at baseline. The morbidity and mortality are recorded in detail. Then, one hundred subjects with high BLL (>20μg/dl) will be randomly assigned to the study and control groups. For 3-6 months, the 50 patients in the study group will receive lead-chelation therapy with calcium disodium EDTA weekly until the BLB falls below BLL< 5 μg/dl, and the 50 control group patients receive weekly placebo for 12 weeks. During the ensuing 18 months, the BLL, biochemical data will be regularly followed up every 3 months. BLL is measured every 6 months. If BLL of the study group patients increase >10 μg/dl, the chelation therapy will be performed again until their BLL is <5 μg/dl. The primary end point is morbidity or mortality during the observation and follow-up period. A secondary end point is the change in hemoglobin, albumin, Cr and Hs CRP during the follow up period.