The case of a 21-month-old girl with lymphoid nodular hyperplasia and the case of a 9-year-old girl with familial adenomatous polyposis are described. Both patients presented rectal bleeding. A defect of secretory IgA was found in the first patient. In both cases diagnosis was based on medical history, barium enema with aircontrast technique, colonscopy, and endoscopic biopsy. Differential diagnosis and diagnostic procedures in these two diseases are discussed.