Substantial progress has been made during the past two years in micro techniques for the detection of metabolic injury due to lead and for the measurement of lead in blood. The pediatrician now has at least one index of absorption and one index of toxicity which can be measured in blood. The report of Piomelli et al.1 on the relationship between the concentration of protoporphyrin (FEP test) and lead in peripheral blood is quite consistent with the reports of Granick et al.2 and Kammholz et al.3; namely, as with other heme precursors,4 there is a statistically significant positive curvilinear relationship between the concentrations of protoporphyrin and lead in peripheral blood.