AIM: To investigate the characteristics of mucosal le-sions and their relation to laboratory data and long-term follow up in breast-fed infants with allergic colitis. METHODS: In this study 31 breast-fed infants were prospectively evaluated (mean age, 17.4 wk) whose rectal bleeding had not ceased after a maternal elimi-nation diet for cow’s milk. Thirty-four age-matched and breast-fed infants (mean age, 16.9 wk) with no rectal bleeding were enrolled for laboratory testing as con-trols. Laboratory findings, colonoscopic and histological characteristics were prospectively evaluated in infants with rectal bleeding. Long-term follow-up with differ-ent nutritional regimes (L-amino-acid based formula or breastfeeding) was also included. RESULTS: Iron deficiency, peripheral eosinophilia andthrombocytosis were significantly higher in patients with allergic colitis in comparison to controls (8.4±3.2 μmol/L vs 13.7±4.7 μmol/L, P<0.001; 0.67±0.49 G/L vs 0.33±0.17 G/L, P<0.001; 474±123 G/L vs 376±89 G/L, P<0.001, respectively). At colonosco-py, lymphonodular hyperplasia or aphthous ulceration were present in 83% of patients. Twenty-two patients were given L-amino acid-based formula and 8 contin-ued the previous feeding. Time to cessation of rectal bleeding was shorter in the special formula feeding group (mean, 1.4 wk; range, 0.5-3 wk) when com-pared with the breast-feeding group (mean, 5.3 wk; range, 2-9 wk). Nevertheless, none of the patients ex-hibited rectal bleeding at the 3-mo visit irrespective of the type of feeding. Peripheral eosinophilia and cessa-tion of rectal bleeding after administration of elemental formula correlated with a higher density of mucosal eosinophils. CONCLUSION: Infant hematochezia, after cow’s milk allergy exclusion, is generally a benign and probably self-limiting disorder despite marked mucosal abnor-mality. Formula feeding results in shorter time to cessa-tion of rectal bleeding; however, breast-feeding should not be discouraged in long-lasting hematochezia. A: To investigate the characteristics of mucosal le-sions and their relation to laboratory data and long-term follow up in breast-fed infants with allergic colitis. METHODS: In this study 31 breast-fed infants were prospectively evaluated (mean age, 17.4 wk) whose rectal bleeding had not ceased after a maternal elimi-nation diet for cow’s milk. Thirty-four age-matched and breast-fed infants (mean age, 16.9 wk) with no rectal bleeding were enrolled for laboratory testing as con-trols . Long-term follow-up with differ-ent nutritional regimes (L-amino-acid based formula or breastfeeding) was also included. RESULTS: Iron deficiency, peripheral eosinophilia and thrombocytosis were significantly higher in patients with allergic colitis in comparison to controls (8.4 ± 3.2 μmol / L vs 13.7 ± 4.7 μmol / L, P <0.001; 0.67 ± 0.49 G / L vs 0.33 ± 0.17 G / L, P <0.001 ; 474 ± ​​123 G / L At colonosco-py, lymphonodular hyperplasia or aphthous ulceration were present in 83% of patients. Twenty-two patients were given L-amino acid-based formula and 8 contin- uous vs. 376 ± 89 G / L, Time to cessation of rectal bleeding was shorter in the special formula feeding group (mean, 1.4 wk; range, 0.5-3 wk) when com-pared with the breast-feeding group (mean, 5.3 wk; range, 2-9 wk). Nevertheless, none of the patients ex-hibited rectal bleeding at the 3-mo visit irrespective of the type of feeding. Peripheral eosinophilia and cessa-tion of rectal bleeding after administration of elemental formula correlated with a higher density of mucosal eosinophils. CONCLUSION: Infant hematochezia, after cow’s milk allergy exclusion, is generally a benign and probably self-limiting disorder despite marked mucosal abnor-mality. However, breast feeding should not be discouraged in long- lastinghematochezia.