There is growing evidence that Helicobacter pylori is responsible for a variety of gastric and duodenal changes which can eventually lead to stomach cancer. Little is known about risk factors for H. pylori infection. We re-analyzed the association of alcohol with H. pylori positivity in 451 conscripts, officers and other military personnel endoscoped due to gastric complaints in the Central Military Hospital of Finland in 1987 and 1988. Serology and culture were done in all patients. Alcohol consumption histories were obtained by use of a self-administered questionnaire. We observed a high odds ratio (OR) of H. pylori infection among young adults who were heavy alcohol consumers compared to non-drinkers (OR 5.32, 95% confidence interval: 1.09-25.95). There was evidence of a dose response when heavy and moderate drinkers were compared to non-drinkers (Mantel-Haenszel chi 2 for trend, p = 0.02) in young adulthood. A subgroup of young respondents who reported drinking all classes of alcohol (including hard liquor) showed an even stronger association and more significant dose-response. Multivariate techniques revealed a qualitative interaction of alcohol with H. pylori positivity in different age groups and among old people an inverse association of H. pylori and alcohol consumption was observed. These findings, if confirmed independently, might have implications for preventing a variety of gastric and duodenal lesions, since they allow identification of high risk groups.