The protective effect of a human strain of Bifidobacterium bifidum (B. bifidum) against murine Group A rotavirus (MRV) was examined in the intestines of BALB/c infected mice. In experiments designed to determine whether B. bifidum mediated MRV shedding during diarrheal disease, pregnant dams (and their expected litters) were randomly assigned to the following groups: 1. Mice infected with MRV alone; 2. B. bifidum treated + MRV infected mice; 3. B. bifidum treated controls; 4. Saline control animals. An enzyme-linked immunosorbent assay (ELISA) for the detection of group A rotavirus was used to measure virus protein. Treatment with B. bifidum significantly reduced shedding of MRV antigen (P < 0.009) days 2-10 post-inoculation. The reduction in shedding of virus protein corresponded well with delayed onset of acute diarrhea (P < 0.02). Closer examination of tissue cross-sections under electron microscopy revealed that the B. bifidum ingested strain adhered to the epithelium of the small intestine. In further experiments, adherent properties of the ingested strain were related to enhancement, although nonsignificant, in immunoglobulin secreting cell responses in Peyer's patch lymphocytes. These results suggest that priming the intestine with B. bifidum is effective against experimental MRV challenge. Closer examination of B. bifidum and related growth factors in suckling neonates on gut physiology and enhancement of local immune responses has potential dietary implications in formulas for newborns.