Human B lymphocytes obtained from healthy donors were infected with Epstein-Barr virus in vitro. From the initiation of infection to the final establishment of a permanent lymphoblastoid cell line, fucosyl glycopeptides of the cell surface were investigated. In order of appearance the following events took place: expression of Epstein-Barr virus-determined nuclear antigen, mitotic activity of the cells and specific glycopeptide alterations on the cell surface. This specific alteration in glycopeptides, as determined by gel filtration, is manifested by the appearance of fast-eluting glycopeptides and was similar to that found on Burkitt lymphoma cells. Neither pokeweed-mitogen-stimulated B lymphocytes nor exponentially growing normal T lymphocytes exposed fast-eluting glycopeptides on their surfaces. Therefore, it is concluded that the appearance of these fast-eluting glycopeptides on the surface of lymphoblastoid cells after EBV infection is not the result of culture conditions or conditions of growth as such. The similarity with glycopeptides derived from Burkitt lymphoma cells, and the observation that a considerable proportion of the B cells becomes immortalized, are discussed.