Peptic ulcer disease mortality patterns of California Japanese are compared with those of their home and host countries for even years from 1960 to 1988, as well as 1989. Data presented are consistent with the hypothesis that Helicobacter pylori is a necessary but not sufficient causal factor in peptide ulcer disease, and that other co-factors including cigarette smoking and salt intake may be important. Deaths due to peptic ulcer numbered 106 among California Japanese, 12,793 for California Caucasians, 107,461 in Japan, and 117,737 for United States Caucasians during the study period. Data for California Japanese were analyzed separately for California Japanese migrants (i.e., those born in Japan) and U.S.-born California Japanese. California Japanese exhibit site-specific peptic ulcer mortality patterns more similar to those of Japan than of the United States. California Japanese migrants (gastric ulcer:duodenal ulcer = 3.2:1), like Japanese in Japan (gastric ulcer:duodenal ulcer = 6.8:1), die more often from gastric than duodenal ulcer, while California and U.S. Caucasians die as often from duodenal ulcer as gastric ulcer (gastric ulcer:duodenal ulcer = 1:1). California Japanese born in the United States exhibit a ratio between those of California Japanese migrants and California Caucasians (gastric ulcer:duodenal ulcer = 2.3:1). U.S.-born California Japanese have the lowest age-adjusted mortality rates for duodenal ulcer and the second-lowest gastric ulcer rates of all populations examined, even though their gastric to duodenal ratio is similar to that for Japan (which has the highest overall ulcer mortality rate).