The immune system of the neonate is influenced by maternal immunity during pregnancy and lactation. An altered microbial exposure, possibly underlying the increase of allergic diseases in affluent societies, may affect maternal breast milk immune composition. Secretory IgA (SIgA), IL-4, IL-10, IL-13, IFN-γ, TGF-β1, and TGF-β2 were analyzed with ELISA in colostrum and 1-mo mature milk from mothers from Estonia (n = 39) and Sweden (n = 60), the two geographically adjacent countries with different living conditions and allergy incidence. The IL-10 and IFN-γ levels were higher in colostrum from Estonian than Swedish mothers, whereas the opposite was true for TGF-β2. In mature milk, higher SIgA and IFN-γ levels but lower TGF-β1 and TGF-β2 levels were observed in Estonian than Swedish mothers. Interestingly, in Sweden but not Estonia, the TGF-β1 and TGF-β2 levels correlated inversely with environmental endotoxin concentrations, whereas positive correlations to microbial load were observed for IL-4, IL-10, and IFN-γ. High colostral IL-13 levels were associated with allergic sensitization during infancy in Sweden. In conclusion, Estonian mothers have lower breast milk levels of TGF-β, particularly TGF-β2, but higher levels of SIgA, IL-10, and IFN-γ than Swedish mothers, possibly because of differences in microbial load.