Objective To explore the genetic polymorphism of the δ aminolevulinate dehydratase (ALAD) gene in children of the Han ethnic group. Methods The erythrocyte σ aminolevulinate dehydratase (ALAD) isozyme phenotypes were determined in a population of 229 pre school and primary school children aged 6～10 years. Results (1) There were 211 individuals with the ALAD 1 1 isozyme phenotype and 18 individuals with the ALAD 1 2 isozyme phenotype. (2) The phenotype of ALAD 2 2 was not detected. Conclusions A polymorphic enzyme exists in the ALAD gene of the Chinese population and the ALAD 2 allele frequency was lower than in Caucasians. Chinese children are genetically less susceptible to lead toxicity than Caucasian children. [