Tandem repeat number polymorphism of a CCTTT pentanucleotide in the promoter region of the inducible nitric oxide synthase gene (iNOS) and a polymorphism of the interleukin-1beta (IL-1B) promoter at position -31 were analyzed in DNA samples from 181 Japanese control subjects and 158 gastric cancer patients, including 96 intestinal type and 62 diffuse type. An association between the intestinal type of gastric adenocarcinoma and higher promoter activity of the iNOS gene was found in women, especially those having higher promoter activity of the IL-1B gene and without a history of smoking. Our results imply that chronic inflammation caused by excess nitric oxide generated by iNOS contributes to Helicobacter pylori-induced gastric cancer.