The relationship between education, social class, smoking habits, alcohol consumption and the risk of digestive tract neoplasms was analysed in a case-control study of 50 cases of cancer of the mouth or pharynx, 209 of the oesophagus, 397 of the stomach, 455 of the colon, 295 of the rectum, 151 of the liver, 214 of the pancreas, and a total of 1944 control subjects admitted for acute, non-neoplastic or digestive tract disorders. Cancers of the mouth or pharynx, oesophagus and stomach were inversely and strongly related to education, with risk estimates ranging between 0.2 and 0.4 for the highest education categories. Significant, but weaker inverse relations were evident for rectal and liver cancer, too, whereas the risk of colon cancer was elevated among more educated individuals. There was no relationship between education and pancreatic cancer. The pattern of risk was largely comparable when the head of the household's occupation was used as indicator of social class. There were strong direct associations between cigarette (as well as pipe or cigar) smoking and cancers of the mouth or pharynx and oesophagus, and a moderate one with pancreatic cancer, but none of the other sites considered was related to smoking habits. Cancers of the mouth or pharynx and oesophagus were independently and strongly related to alcohol consumption, too, while the associations between alcohol and liver or pancreatic cancer were moderate and not significant. Cancers of the stomach, colon and rectum were unrelated to measures of alcohol consumption.