Transforming growth factor (TGF)-beta has a crucial effect on IgA production, which is the major humoral effector of mucosal immunity. Breast milk contains the abundant amount of TGF-beta in the early period of lactation. AIM-STUDY DESIGN: To verify the notion that TGF-beta in breast milk might contribute to the development of IgA production in newborns, we investigated the association of TGF-beta in maternal colostrum with an increase of serum IgA in newborns during the first month of life.The concentrations of TGF-beta1 and TGF-beta2, including IL-6 and IL-10, in colostrum samples from 55 healthy mothers were determined by ELISA. The levels of IgA and IgM in serum samples collected from corresponding newborn babies at birth and at 1 month of age were measured by ELISA.TGF-beta1 and TGF-beta2 were detected in substantial quantities in all colostrum samples, but IL-6 and IL-10 were present only in a proportion of samples. An increase of serum IgA in newborn during the first month of life was significantly higher than that of serum IgM (p<0.001). Notably, an increase of serum IgA in newborns during 1 month of life was well correlated with levels of both TGF-beta1 (r=0.38, p=0.005) and TGF-beta2 (r=0.45, p=0.0005) in colostrum, while that of IgM was marginally correlated with colostral TGF-beta2 (r=0.28, p=0.04). The association of increase of serum IgA in newborns with IL-6 and IL-10 in colostrum was not evident.Our findings suggest that TGF-beta in colostrum might serve as the starter of IgA production in newborn infants.