OBJECT: The aim of this study was to determine the bone lead concentration in lead smelters and reference subjects, relate them to the lead concentration in blood (B-Pb) and urine (U-Pb), and to use the measured bone lead to calculate a biological half-life for lead in bone. METHOD AND DESIGN: The lead concentration in the second phalanx of the left index finger (bone-Pb) was determined in vivo using an X-ray fluorescence technique. The study population comprised 89 smelters with a history of long-term exposure to lead (71 active and 18 retired) and 35 reference subjects (27 active and 8 retired) with no known occupational exposure to lead. Bone-Pb was related to the previous lead exposure, estimated as a time-integrated B-Pb (CBLI). RESULTS: The retired smelters had the highest bone-Pb (median value 55 micrograms/g wet weight, as against 23 micrograms/g in active smelters) and 3 micrograms/g in the reference subjects. A strong positive correlation was observed between the bone-Pb and the CBLI among both active (rs = 0.73; P