The association of blood lead and iron status with erythrocyte protoporphyrin (EP) levels for the United States population between the ages of 6 months and 74 years was examined. The data for blood lead level (BLL), EP, transferrin saturation (TS), and total iron binding capacity (IBC) were obtained from the second National Health and Nutrition Examination Survey (NHANES-II). The BLL varied from the high mean value of 16.9 micrograms/deciliter microg/dl) in 18 to 74 year old men to the low value of 11.8 microg/dl in women in the same age bracket. The EP concentration was the highest, 25.1 micrg/dl, in 6 month to 2 year old children, and the lowest, 20.7microg/dl in the 6 to 17 year old group. The percentage of TS varied from the high value of 29.5 microg/dl in 18 to 74 year old men to the low value of 13.5 microg/dl in the young children population. The mean IBC was 410.7 in toddlers and 362.6microg/dl in the 18 to 74 age group of men. The levels for 3 to 5 year old, 6 to 17 year old, and for 18 to 74 year old women were within the reported values for toddlers and adult men. The percentage of persons with elevated EP was the highest among those with low iron and high lead levels. Persons with iron deficiency were more vulnerable to lead exposure. A combination of blood level measurement and EP determination would represent a more accurate and effective method for identifying children who are at the greatest risk of lead toxicity or iron deficiency. The authors state that EP levels above 30microg/dl are significantly more prevalent in the 6 month to 5 year age group, with blood lead concentrations of 20 to 29microg/dL, than in those with lower lead content.