OBJECTIVE: To investigate the causes of haematochezia in exclusively breast fed infants. METHODS: Seventy-five babies presenting with haematochezia were enrolled. These babies were exclusively breast fed. The age of haematochezia occurrence, concomitant symptoms and laboratory findings (including routine blood test, routine stool test, liver function, stool culture, colonoscopy and histological examination) were recorded. The mothers of the 75 babies were given a diet without animal and floristic proteins for four weeks. The symptoms of haematochzia in the babies were observed after maternal protein-free diets. RESULTS: Haematochezia occurred at an average age of 7.4 weeks. Diarrhea was the most common concomitant symptom (71%). The laboratory testing showed that mild anaemia was the most common (60%). Red cells and white cells were found in the routine stool test. Stool culture was negative. Colonitis was proved through colonoscopy. Twenty babies underwent histological examinations and eosinophilia was noted. Gross hematochezia disappeared 72-96 hrs after maternal protein-free diets. CONCLUSIONS: Exclusively breast fed infants may be sensitive to protein taken by their mothers and may appear with haematochazia.