The milk fermented by Bifidobacterium longum gave better results than yogurt against diarrhea in children, after the use of the antibiotic erythromycin; more than that, the fermented milk is active against Rotavirus infection. The most relevant fact of this experiment is primarily that it has a positive activity in reducing Escherichia coli and Clostridium perfringens by metabolites (glycoprotein) formed during fermentation of milk with Bifidobacterium longum.