In the paper the degree of lead micro-intoxication was assessed in school children from the region of emissions of the Mining-Ironworks Complex "Bolesław" in Bukowno. The study included 323 children of either sex aged from 7 to 14 years. In these children the levels of selected lead intoxication markers were determined--concentration of zinc protoporphyrin (ZnPP) in the erythrocytes and concentration of delta-amino-laevulinic acid (ALA) in urine. The obtained results were compared with corresponding results in the control group which consisted of 163 children of the same age, living in a control area without exposure to heavy metals. In the studied group in all age subgroups, significantly higher ALA concentrations in urine were observed in comparison to the control group. At the same time, exceeding of upper acceptable range of ALA concentration in the organism was five times more frequent in this group. On the other hand, the concentration of ZnPP in the erythrocytes failed to show any significant differences between the compared groups in any of the analysed age subgroups. On the basis of the obtained results it was demonstrated that the school children living in the region of emissions of the MIC "Bolesław" had biochemical features of long-term lead microintoxication. As it seems, the concentration of ALA in urine is of greater diagnostic value in comparison to the concentration of ZnPP in the erythrocytes in screening examinations in these children.