Previous studies in Ghana had shown that primary infections with Epstein-Barr virus in infants under the age of two years remain silent and evoke antibody responses different from those seen in infectious mononucleosis. In order to determine whether or not these observations were limited to Africa, 80 American infants presenting with minor infectious complaints were studied serologically; 14 (17.5%) showed evidence of recent or current primary infections with Epstein-Barr virus. The clinical features of these 14 infants were similar to those of the other 66 and did not suggest a diagnosis of infectious mononucleosis, nor were there histories of a recent infectious mononucleosis-like illness. Ten (72%) had antibodies to the early antigen complex induced by Epstein-Barr virus; however, these antibodies were directed, as in the Ghanaian infants, against the restricted rather than the diffuse components, in contrast to the pattern generally observed in infectious mononucleosis. Possible reasons for the differences between the responses of infants and those of older individuals to primary infection with Epstein-Barr virus and to the early antigen complex are discussed.