The Epstein-Barr virus (EBV) gH-gL complex includes a third glycoprotein, gp42. gp42 binds to HLA class II on the surfaces of B lymphocytes, and this interaction is essential for infection of the B cell. We report here that, in contrast, gp42 is dispensable for infection of epithelial cell line SVKCR2. A soluble form of gp42, gp42.Fc, can, however, inhibit infection of both cell types. Soluble gp42 can interact with EBV gH and gL and can rescue the ability of virus lacking gp42 to transform B cells, suggesting that a gH-gL-gp42.Fc complex can be formed by extrinsic addition of the soluble protein. Truncated forms of gp42.Fc that retain the ability to bind HLA class II but that cannot interact with gH and gL still inhibit B-cell infection by wild-type virus but cannot inhibit infection of SVKCR2 cells or rescue the ability of recombinant gp42-negative virus to transform B cells. An analysis of wild-type virions indicates the presence of more gH and gL than gp42. To explain these results, we describe a model in which wild-type EBV virions are proposed to contain two types of gH-gL complexes, one that includes gp42 and one that does not. We further propose that these two forms of the complex have mutually exclusive abilities to mediate the infection of B cells and epithelial cells. Conversion of one to the other concurrently alters the ability of virus to infect each cell type. The model also suggests that epithelial cells may express a molecule that serves the same cofactor function for this cell type as HLA class II does for B cells and that the gH-gL complex interacts directly with this putative epithelial cofactor.