OCCULT gastrointestinal bleeding has been previously reported to be a common complication in patients with the clinical diagnosis of aortic stenosis.1-3 To further define this possible relationship, a group of patients in which the diagnosis of aortic valve disease had been proven surgically was reviewed. Patients The group of patients consists of 211 with aortic valve replacements for aortic stenosis or regurgitation or both and 110 with mitral valve replacements for mitral stenosis or regurgitation or both who were operated on from July 1963 to December 1966 at the Massachusetts General Hospital. The cases of mitral replacements were reviewed to provide a similarly ill group of patients as a reasonably comparable control group for those with aortic stenosis. The gastrointestinal bleeding was considered significant if four consecutive guaiac stool examinations were positive with or without hematemesis, drop in the hematocrit reading, or necessity for transfusion. Only those patients