We present nine exclusively breast-fed, full-term infants with mild re
ctal bleeding due to proctocolitis. The mean age at the onset of sympt
oms was 5 weeks (range 1-8 weeks). Rectosigmoidoscopic examination was
performed in all children within 2 days after admission, showing infl
ammatory changes such as oedematous mucosa with petechial haemorrhages
. Rectal mucosal biopsy specimens were obtained in eight cases and rev
ealed intra-epithelial eosinophilic granulocytes in seven and a diffus
e increase of eosinophils in the lamina propria in six. Allergy to cow
's milk protein transferred to the infants via the breast milk was bel
ieved to be the cause of the inflammation. The intake of cow's milk pr
otein was then restricted in seven mothers. Following this regimen, sy
mptoms were relieved within 4 weeks in the six infants who were seen a
t follow up, One child recovered spontaneously without dietary restric
tions. Considering the beneficial effect of the diet regimen in additi
on to the histological findings, allergy to cow's milk protein is poss
ibly the aetiology of the proctocolitis seen in these nine exclusively
breast-fed babies, although no challenge tests were performed to conf
irm this suspicion, Conclusion This report shows that proctocolitis oc
curs in exclusively breast-fed infants. It is speculated that allergy
to cow's milk protein may have played a role in the pathogenesis.