The aim of this study was to determine whether reduced pulmonary function is an independent risk factor for peptic ulcer. Among 5933 Japanese men studied in Hawaii, 243 developed gastric ulcers and 99 developed duodenal ulcers 20 yr after an examination completed in 1968. The examination included measurement of forced expiratory volume in 1 s and a detailed smoking history. The percent predicted forced expiratory volume was significantly and inversely related to ulcer incidence, but not after adjustment for smoking or among those who had never smoked. Cigarettes were associated with increased ulcer risk in both stomach and duodenum but showed a dose-response in pack years only for gastric ulcer. We conclude that the association of reduced pulmonary function with peptic ulcer in the Japanese in Hawaii is largely attributable to smoking and that smoking is more strongly related to gastric than duodenal ulcer. The especially strong link between cigarettes and gastric ulcer suggests that decreased smoking or synchronous decrease in cigarette tar content may have contributed to the recent unexplained decrease in male gastric ulcer.