Maternal antibodies against measles in 223 healthy children aged 22 to 31 weeks were studied. The ratio of children with detectable antibodies declined from 61.4 percent at 22-23 weeks of age to 20 percent at 26-27 weeks of age. Since the minimum proportion of antibody-positive children (15.6% at 26-27 weeks of age) is still higher than the optimum proportion (5%), the Schwarz vaccine which is used mostly in measles immunization seems not to be effective to obtain a high seroconversion rate in our infants. We suggest that the Edmonston-Zagreb strain of measles vaccine be used for infants under 9 months of age in Turkey.