• Lead poisoning Is treated with chelating agents. We report the natural decline of blood lead (Pb-B) concentration after treatment(s) (1967 to 1972) In 74 patients whose maximal Pb-B level ranged from 100 to 471 μg/dL (4.83 to 22.73 μmol/L). These longitudinal data (range, nine to 17 years) disclose a predictable decrease in Pb-B levels after treatment that is independent of the maximal Pb-B level before therapy. The correlation between age in months and the logarithm of the Pb-B level was significant, and the equation defined by the regression line allows one to predict Pb-B levels at specific ages after chelation therapy. It is important to recognize the slow, natural decline of Pb-B levels after chelation therapy once the level is stable and below 70 μg/dL (3.38 μmol/L). Multiple repeated courses of calcium disodium edetate are unlikely to influence the natural decline of the Pb-B level in asymptomatic children.