Case history is reported of an infant who was changed from breast to bottle feeding at fourth day of life, who on ninth day developed bilious vomiting and bloody diarrhoea. Later gas was found in colonic wall on X-ray. Necrotizing enterocolitis was diagnosed and infant managed with total intravenous alimentation. On recovery although she tolerated breast milk, return to cow's milk formula lead to return of bloody diarrhoea. Subsequently she thrived on a cow's milk-free diet based on chicken meat formula. At four months after total of 15 ml cow's milk she had an acute anaphylactic reaction. She recovered and is well on milk-free diet. Thus, this infant has recovered from necrotizing enterocolitis but has evidence of persistent cow's milk protein intolerance. The hypothesis is put forward that in this child cow's milk protein played a major role in the pathogenesis of necrotizing enterocolitis.