It has been suggested that the measurement of the degree of inhibition of red blood cell (RBC) δ-aminolevulinic acid dehydrase (ALAD) activity is a useful indicator for the detection of children with increased lead absorption. Twenty children had simultaneous measurements of blood lead and RBC-ALAD activity, and then received chelation treatment with edetic acid (EDTA). The inhibition of RBC-ALAD activity was found to be highly correlated with the amount of lead excreted in the urine. In this study, the measurement of RBC-ALAD appeared to be superior to the measurement of blood lead in identifying those children with an increased burden of "chelatable" lead.