A study of the small intestine in patients with rheumatoid arthritis was undertaken because it has been suggested that the disease arises secondary to hereditary enteropathy. No abnormality of jejunal mucosa was detected histologically in five patients with arthritis, and studies of bowel function were normal in six patients. No serologic evidence of increased intestinal permeability, as indicated by antimilk or antijejunal cell antibodies, was detected in sera of 17 arthritic patients. Gluten-free diet, claimed to be helpful in treating the disease, proved of no value in a brief, carefully controlled, hospital trial in five patients.