In this study, we evaluated the effects of the genetic polymorphism of ALDH2 (low Km aldehyde dehydrogenase) on toluene metabolism and determined biological exposure indices (BEIs) of the genotypes of ALDH2. The study subjects included 45 toluene workers and 122 nonexposed students. The genotype of ALDH2 was classified into the homozygous genotype of normal ALDH2 (NN), the homozygous genotype of an inactive one (DD), and the heterozygous genotype of normal and inactive ones (ND) by means of artificial-RFLP. The personal exposure levels to toluene were monitored, using diffusion type samplers and urinary hippuric acid (HA) and creatine concentrations were determined. The urinary HA levels of the three genotypes of ALDH2 of nonexposed students did not differ. In the toluene workers, positive correlations between the personal exposure to toluene and urinary HA levels were observed in the NN, ND, and DD groups. The urinary HA level of the DD group was significantly lower than that of the NN or ND group. Regression lines were used to estimate the BEIs of the NN, ND, and DD groups, which were approximately 2.9 g/g creatinine, 3.3 g/g creatinine, and 1.9 g/g creatinine, respectively.