. Operations were performed on 2,956 patients during the study period. The incidence of upper gastrointestinal bleeding was 0.9%. Twenty (77%) of the 26 patients with upper gastrointestinal bleeding and 145 (63%) patients of the control group had serologic evidence for H. pylori infection (odds ratio, 1.9; 95% confidence interval 0.7-5.0; p = .2). Patients who required prolonged mechanical ventilation had a significantly greater risk for upper gastrointestinal bleeding (odds ratio, 22