Single-nucleotide polymorphisms (SNP) in genes coding metabolizing enzymes modulate gene functions and cellular toxicity in response to chemicals. Quinone oxidoreductase 1 (NQO1) is an important detoxification enzyme involved in the catabolism of 1,4-benzoquinone (1,4-BQ), a benzene metabolite believed to be associated with bone-marrow toxicity and leukemia. Gene function was evaluated in immortalized human B lymphocytes derived from a Chinese Han population with independent genotypes at 2 NQO1 SNP sites. 1,4-Benzoquinone was incubated with these immortalized lymphocytes of differing genotypes. Among the genotypes of 2 SNP examined, cell lines with rs1800566CC showed a higher NQO1 enzymic activity after a 48 h of treatment with 10 muM 1,4-BQ, and a lower comet rate compared with cells of CT/TT genotypes. Data suggested that NQO1 rs1800566 might serve as a functional genetic marker for benzene toxicity in the Chinese Han population. The immortalized B lymphocytes derived from different populations might thus be used as a biomarker to detect functional genetic markers related to exposure to environmental chemicals.