The purpose of this paper was to concisely review the practical changes in MeHg concentrations in fetus and offspring throughout gestation and suckling from our recent animal and human studies. In the animal study, adult female rats were given a diet containing 5ug/g Hg (as MeHg) for 8 weeks. Then they were mated and subsequently given the same diet throughout gestation and suckling. On embryonic days 18, 20, 22 and at parturition, the concentrations of Hg in the brains of fetus were approximately 1.5-2.0 times higher than those in the mothers. However, during the suckling period Hg concentrations in the brain rapidly declined to about 1/10 of that during late pregnancy. Hg concentrations in blood also decreased rapidly after birth. In human study, Hg concentrations in red blood cells (RBC-Hg) in 16 pairs of maternal and umbilical cord blood samples were compared at birth and 3 months of age after parturition. RBC-Hg in the umbilical cords was about 1.6 times higher than those in the mothers at parturition. However, all the infants showed declines in Hg concentrations throughout the breast-feeding period. RBC-Hg at 3 months of age was about half that at birth. Both the animal and human studies indicated that MeHg exposure to the fetus might be especially high but it dramatically decreases during the suckling period. Therefore, close attention should be paid to the gestation rather than the breast-feeding period to avoid the risk of MeHg to human infants.