This study describes a group of 34 infants under 1 1/2 months of age presenting with isolated rectal bleeding not related to hemorrhagic disease of the newborn or to campylobacter infection and with spontaneously favorable evolution. Systematic rectosigmoidoscopy showed the presence of mucosal alterations in the form of either longitudinally stretched ecchymoses lying on a normal mucosa or diffuse ecchymotic patches dispersed on a congestive and friable mucosa, rarely associated to visible micro-ulcerations. Biopsies showed mucosal hemorrhage, capillary vessel congestion, and epithelial erosions, as well as various grades of inflammation. Clinical data indicate that this hemorrhagic colitis is a heterogeneous group where dietary protein intolerance may account for some cases.