Int. J. Environ. Res. Public Health 2009, 6 1000 significantly associated with the blood lead concentration, even in the environmental lead exposed subjects. Further confirmation with a large sample size is needed. Keywords: ALAD gene; blood lead level; environmentally lead exposure; Japanese. 1. Introduction From the public health point of view, inorganic lead exposure has been a serious problem, not only in the occupational but also in environmental settings [1]. Lead toxication can cause many diseases such as kidney damage [2,3], reproductive system toxicity [4], hypertension [5], and alterations in cognitive development in children, even at low doses [6-8]. Estimation of the health risks associated with low-level exposures to lead has important implications with respect to its regulation. Health-based guidelines limiting occupational and environmental exposures to lead have become more stringent and are now thought to protect most of population against major adverse health effects. Recently the United States Centers for Disease Control and Prevention also recommended the reduction of lead concentrations <10 g/dL to prevent lead toxicity for children under 6 years old [9]. However, genetically susceptible individuals may not be fully protected by current regulatory standards, so the discovery of genetic factors that might influence susceptibility to lead-induced intoxication could have significant public health ramifications [10]. Polymorphisms of the ALAD gene have been associated with the accumulation of lead in the blood, bone, and internal organs [10], and might differentially predispose for psychiatric symptoms in individuals exposed to lead [11]. Many reports have suggested that the ALAD2 allele may exert protective measures against the neurotoxic effects of lead [12-15]. However, the subjects of these reports have typically been occupationally exposed workers, and no firm evidence exists for an association between ALAD genotype and susceptibility to lead toxicity under environmental exposure levels. The objective of this study examined the relationship between ALAD1, ALAD2 genotypes and blood lead level among workers who were not occupationally exposed to lead. 2. Methodology 2.1. Subjects We explained this study to Japanese healthy workers from a Japanese chemical industry company located in Kanagawa prefecture, and received a written informed consent from each participant. A total of 101 healthy workers (73 men and 28 women, after exclusion of those who occupationally handled or used to handle lead in their lives) were subjected to medical examination and genotyping. Among these,