To clarify the role of antibody dependent cell-mediated cytotoxicity (ADCC) in the prevention of measles virus infection during the first year of life, ADCC activities in cord blood and peripheral blood of infants were examined by a (51)Cr-release assay method. Transmission of ADCC from the mother to the newborn was also evaluated.ADCC activities in the cord blood were demonstrated in 40 among 41 newborns whose mothers had a history of measles infection. A significant correlation in ADCC activities between cord blood and maternal blood was found (r=0.946). The antibody which mediates ADCC correlated with neither NT antibody nor HI antibody against measles virus in the cord blood. Thus, this antibody represented another group of antibody. HI antibody disappeared from the age of 6 months, while the antibody mediating ADCC remained until the age of 12 months. ADCC activities were detected even in the cord blood of newborns whose mothers were infected with measles 16 to 28 years ago. These results suggest that the antibody mediating ADCC against measles virus is transmitted from the mother to cord blood via the placenta. Furthermore, ADCC appears to play an important role in preventing the infection of infants between 6 to 12 months of age with measles virus.