The Kehoe Pb balance experiments were carried out from 1937 to 1972 and involved over 21,000 d of measured exposure of Pb in humans. Pb balance and Pb in the diet, feces, urine, and blood were measured under normal conditions and during periods of oral and airborne Pb supplementation. Considerable natural variability was seen throughout the experimental periods, due primarily to variations in dietary Pb. The overall mean blood Pb concentration for all subjects was 25 μg per 100 g, with individual control means ranging from 18 to 40 μg per 100 g. Urinary Pb averaged 29 μg/l overall, with individual control means ranging from 19 to 45 μg/l. The overall average diet contained 181 μg/d (159 μg/d based on median data); however, the mean dietary Pb for the individual control periods decreased from approximately 300 μg/d in 1937 to 100 μg/d in 1970. Fecal Pb had an overall mean of 225 μg/d (212 μg/d based on median data) on a per‐sample basis, which exceeded the dietary Pb average because most subjects did not defecate daily. Averaged over the entire control period, fecal Pb was 196 μg/d, still in excess of the overall average diet. Pb balance was calculated as dietary Pb minus Pb in the feces and urine and did not include an estimate of inhaled Pb. Although three subjects were in positive balance during their control periods, the overall average balance was —32 μg/d, ranging from —106 to +25 μg/d for individual control periods. The balance data indicate that an appreciable amount of Pb absorbed from the air was excreted. Ingestion experiments involved daily supplements of 300, 1000, 2000, and 3000 μg Pb per day. Except for subject SW, who received the 300 μg supplementation, all subjects experienced increased Pb in the blood, urine, feces, and body burden proportional to the ingested Pb. For SW, blood and urine Pb did not increase even though body and fecal Pb did. Overall, the feces, blood, urine, and balance increased by 0.83 μg/d, 0.017 μg per 100g, 0.045 μg/d, and 0.133 μg/d for each increase of 1 μg Pb in the diet. Inhalation exposure experiments involved chamber concentrations of 10, 20, 75, and 150 μg/m3 for varying exposure times. Overall chamber exposure rates ranged from 0.6 to 35.9 μg/m3, averaged over the entire exposure period. The influence of natural variability of dietary Pb permeated all inhalation experimental periods and tended to override the responses of blood, urinary, and fecal Pb at adjusted exposure rates below 10 μg/m3 (below chamber concentrations of 75 μg/m3). Overall, the blood, urine, and feces increased by 0.57 μg per 100 g, 1.41 μg/d and 1.47 μg/d for each increase of 7 μg/m3 Pb in the air. All subjects who experienced obvious increases in body Pb during their exposure periods showed obvious and prompt body Pb washout during postexposure periods.