The retention and tissue distribution of210Pb were studied in 10‐day‐old, 150‐day‐old, and adult monkeys. Lead‐210 nitrate was administered to the monkeys by gavage after a 12 hr fast and210Pb excreted in urine and feces was monitored for 96 hr. All monkeys were necropsied 96 hr after dosing and the210Pb concentration of various tissues was determined. The data demonstrated that infant monkeys retained 64.5 and 69.8% of the orally administered210Pb at 70 and 150 days of age, respectively, while adult monkeys retained 3.2% of the210Pb dose. Blood210Pb levels 96 hr after dosing did not vary significantly between age groups. Of the210Pb contained in blood, 98–99% was found in blood cells and 1–2% in blood plasma; 5–8% of the Pb in blood cells was bound to blood cell membranes. None of these parameters varied significantly with age. The percentage of the lead dose excreted in urine did not vary significantly between age groups. Analysis of tissues for210Pb revealed that both the tissue Pb concentrations and tissue Pb:blood Pb ratios were significantly higher in the bone structure of infants than adults. Brain Pb:blood Pb ratios were significantly greater in 10‐day‐old infants than 150‐day‐old infants or adults.