Zinc protoporphyrin (ZPP) is generated in the erythrocytes of patients with lead toxication and iron deficiency anemia by the incorporation of zinc instead of ferrous iron into protoporphyrin. Although the measurement of ZPP has been thought to be a potential screening test for evaluating iron deficiency, no simple and reliable ZPP assay method has been available until recently. A newly developed hematofluorometer allows us to quickly determine the level of ZPP in a drop of unprocessed whole blood. In this study, we measured the concentration of ZPP in 732 children including 22 patients with iron deficiency anemia using this hematofluorometer. The cut off value of whole blood ZPP in children was determined to be 38.2 micrograms ZPP/dl whole blood. The level of ZPP showed a good negative correlation with the concentration of hemoglobin. The specificity and the sensitivity of this assay were 97.2% and 81.8%, respectively. These results indicate that this ZPP assay using the newly-developed hematofluorometer is a practical way to screen for iron deficiency anemia.