Cytomegalovirus antibodies have been determined by indirect hemagglutination technique in sera taken during the first year of life in two infant groups : Bantu infants in Mozambique, French infants in Alsace. IgM specific antibodies have been detected in serum fractions obtained by density gradients. The evolutions of maternal antibodies and of antibodies resulting from a primary CMV infection have been documented. The analysis of the results confirmed that the mother is the main source of infection and that contamination occurs at the time of birth.