Abstract
The relationship between blood lead and free erythrocyte protoporphyrin (FEP) or zinc protoporphyrin (ZPP) was evaluated prospectively for 50 weeks in a group of workers who were removed from occupational lead exposure for 10 weeks. FEP or ZPP continued to fall in spite of a rising blood lead upon re-exposure. Although statistically significant relationships between square root FEP or ZPP and blood lead were found, wide confidence limits prevent meaningful predictions of blood lead from FEP or ZPP for an individual. Blood lead is a better index of exposure than FEP or ZPP, especially when exposure is not stable.