To assess the association between NAD(P)H: quinone oxidoreductase 1 (NQO1) C609 T allele and apolipoprotein E (ApoE) polymorphism and sporadic Alzheimer disease (SAD).The polymorphisms of NQO1 and ApoE gene were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method in 92 SAD patients and 108 normal controls, all of Han nationality.The frequencies of mutant T allele and T/C + T/T genotype at nucleotide position 609 of NQO1 gene were 56% and 89% respectively in the patients with SAD, significantly higher than those in the controls (45% and 71% respectively) with an odds ratio of 1.56 (for mutant T allele) and of 3.301 (for genotype) respectively. The frequency of the ApoE2 allele was significantly lower in the SAD patients than in the controls (chi(2) = 3.753, P < 0.05) and the frequency of ApoE4 was higher in the SAD patients, however, without a statistically significant difference (chi(2) = 1.863, P = 0.172). No significant interaction was found between NQO1 C609T and ApoE polymorphisms in SAD patients.NQO1 C609T may be an independent genetic risk factor for SAD in Chinese.