The effects of environmental exposures on the development of gastric and duodenal ulcers were investigated in a prospective study of 7,624 American men of Japanese ancestry in Hawaii. After 149,291 person-years of observation, there were 280 incident cases of gastric ulcer and 149 incident cases of duodenal ulcer. The risk of both gastric and duodenal ulcers progressively increased with increasing pack-years of cigarette smoking. In contrast, alcohol intake was not associated with either type of ulcer. The risk of gastric ulcer was positively associated with the use of table salt/soy sauce, but there was no association with the consumption of other oriental foods. The risk of duodenal ulcer was inversely associated with western style diet around 1940 and with bread intake of two or more servings per day. The authors did not find any protective or adverse effect of milk and fruit consumption on peptic ulcer risk.