Abstract: Associations betweenδ-aminolevulinic acid dehydratase(ALAD)polymorphism and lead-induced neurotoxicity were investigated among 179 children whom have been living in lead polluted environment.The authors examined associations of ALAD genotype with blood lead and zinc protoporphyrin(ZPP)levels,intelligence quotient(IQ),choice reaction time.Comparing with ALAD121 genotype,the ALAD1-2 genotype had slight increased blood lead and ZPP levels but there were not significantly differences.The subject with ALAD1-2 genotype had slowly reactive time in choice reaction test(P=0.02).No differences between genotypes were found for body weight,high,hemoglobin and IQ.When the blood lead level was adjusted by covariance analysis,reactive time in choice reaction test of the ALAD1-2 genotype was closed to that of ALAD1-1 homozygote.The results suggest that ALAD1-2 subjects respond differently to lead-induced neurotoxic effects,the mechanism maybe relate to gene-mediated increased lead load in body.