In order to study the placental transfer of mercury compounds and their accumulation in fetus in normal maternal body, total mercury and methylmercury contents in maternal blood, placenta, and umbilical cord blood were examined in 89 women after normal delivery, living in Nagoya city, and the following results were obtained. 1) In methylmercury content, there was a highly significant correlation between maternal blood and placenta but highly significant correlation was not found between them for total mercury content. 2) There was highly significant correlation in methylmercury content between placenta and umbilical cord blood. 3) There was a highly significant correlation in total mercury and methylmercury contents in blood, between maternal blood and umbilical cord blood. It was concluded that mercury compounds, especially methylmercury compounds, transferred through the placenta to fetus and accumlated there, and that higher intake of mercury compounds into the maternal body resulted in the higher mercury content in umbilical cord blood.