Risk factors for prepyloric and duodenal ulcer were analysed by means of a questionnaire in 132 patients and 132 population controls, pairwise matched for age and sex. Several factors associated with a lower socioeconomic status, such as short education, low income and low housing standard, and a job characterized by low satisfaction, low demands, and low autonomy, were more prevalent among the patients. The odds ratio (OR) with 95% confidence limits (CL) in smokers versus non-smokers was 2.9 (CL, 1.7-5.0). A trend emerged in relation to the daily number of cigarettes, with an OR of 4.1 (CL, 2.2-7.5) for those smoking more than 10 cigarettes. The risk of having peptic ulcer disease was virtually unrelated to other psychiatric and somatic morbidity, to marital status, personal worries, type-A behaviour, experience of a hectic or psychologically demanding job, and to consumption of coffee, alcohol, and drugs. Our data lend no support to the concept that peptic ulcer disease is a disorder related to psychologic stress. Causative agents other than smoking should probably be sought among factors characterizing the life style of low socioeconomic classes.