We enumerated the predominant gut genera from fecal samples of nine healthy and eight milk-hypersensitive adults both before and after 4 weeks Lactobacillus rhamnosus GG (LGG) supplementation. The anaerobic intestinal microflora of milk-hypersensitive adults was found to resemble that of healthy adults. LGG-consumption resulted in a significant increase in the number of bifidobacteria in healthy but not in milk-hypersensitive subjects, as well as a general increase in bacterial numbers in all other bacterial genera tested in both groups. In conclusion, the composition of the gut microbiota in milk-hypersensitive adults appears to be normal. LGG may have potential in reinforcing the endogenous flora.