Lactobacillus rhamnosus GG is one of the most characterized and utilized probiotic strains, with numerous clinical trials across all ages. It is a human origin strain, identified for its resistance to gastric acidity, adhesion properties, and ability to support healthy gut microflora. Studies involving infants and children suggest that supplementation with L. rhamnosus GG supports healthy G.I. colonization, G.I. function, and immune function, particularly related to skin and respiratory health. In a study involving children ages 1-7 attending day care, L. rhamnosus GG offered statistically significant support for respiratory and immune health. Studies involving pregnant women suggest supplementation supports healthy gut microflora in the infant, and nutrient metabolism during pregnancy. In one study, infants whose mothers had received L. rhamnosus GG during pregnancy showed increased bifidobacterial diversity at Day 5 after birth. L. rhamnosus GG is well known for its effects on bowel function, particularly abdominal comfort, bowel motility and occasional diarrhea. It also promotes cytokine balance in the G.I. tract at the level of gene expression, and overall immunomodulatory support. In a double-blind, crossover study, L. rhamnosus GG supplementation moderated the neutrophil and monocyte immune response in dairy-challenged, milk-sensitive subjects, while promoting immune function in non-sensitive subjects. In another study, L. rhamnosus GG promoted healthy gene expression to support white blood cell (WBC) function. Elderly subjects supplemented for 28 days showed 95 differentially expressed genes related to cellular movement, cell-to-cell signaling, and cytokine response.‡