Alterations in DNA methylation have been associated with cancers at almost all tumor sites and represent one of the most consistent changes in neoplastic cells. The underlying etiological mechanisms for alteration of DNA methylation patterns are not understood, but experimental studies in animals suggest potential environmental and genetic influences. The purpose of this study was to investigate whether DNA hypomethylation in peripheral blood DNA (potentially representing status at the lung) was associated with increased risk for the development of lung cancer. We evaluated genome-wide and p53 gene-specific hypomethylation in 100 lung cancer cases and controls selected from a large clinical trial of male smokers, the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study. Genome-wide methylation status was assessed using the in vitro methyl acceptance capacity assay and p53 gene-specific methylation status using the HpaII quantitative PCR assay. Hypomethylation was evaluated as a risk factor using multivariate conditional logistic regression analyses. Genome-wide methylation status was unrelated to lung cancer risk; the odds ratio was 1.25 and the 95% confidence interval was 0.48-3.21 for those in the highest versus lowest quartile of hypomethylation status. Hypomethylation of the p53 gene in exons 5-8, the hypermutable region, was associated with a 2-fold increased risk for lung cancer (odds ratio, 2.20; 95% confidence interval, 1.04-4.65), whereas there was no risk increase for hypomethylation at exons 2-4, a region of the gene not known for its mutability or functional significance in cancer. Our results indicate that hypomethylation status within exons 5-8 of p53 from peripheral lymphocyte DNA may be a relevant predictor of lung cancer among male smokers.