A simultaneous case-control study on stomach cancer and colo-rectal cancer involving 93 cases with stomach cancer, 93 cases with colo-rectal cancer and 186 controls was conducted using a common questionnaire at the Aichi Cancer Center Hospital in 1981-83. A fondness for salty tastes, especially salted foods such as pickled hakusai (vegetable) and dried & salted fishes, which are typical traditional Japanese foods showed a significantly positive association with stomach cancer (relative risk(RR) = 2.60, P less than 0.01). On the other hand, the habit of eating a western-style breakfast, particularly for 10 years or more made a significant contribution to the risk of colon cancer (RR = 2.24, P less than 0.05) but conversely decreased the risk of stomach cancer (RR = 0.50, not significant (NS)) and rectal cancer (RR = 0.40, NS). In this study, relatively frequent intakes (4 times/week) of some vegetables, i.e. pumpkin, green pepper, onion and cabbage, showed high relative risks for both stomach and colon cancers, contrary to the findings of previous epidemiological studies. Cigarette smoking increased the risk of stomach cancer (RR = 1.99, NS) but decreased that of colon cancer (RR = 0.61, NS). There was no positive relation between drinking and cancer at any site. Some other factors with opposite effects on the two contrasting cancers and some independent factors were identified in this comparative case-control study.