The primate type C retrovirus gibbon ape leukemia virus (GaLV) has been shown to use a widely expressed, multiple membrane-spanning protein of unknown function as its cell surface receptor on human cells (GLVR1) (Johann, S. V., Gibbons, J. J., and O'Hara, B. (1992) J. Virol. 66, 1635-1640; O'Hara, B., Johann, S. V., Klinger, H. P., Blair, D. G., Rubinson, H., Dunni, K.J., Sass, P., Vitek, S. M., and Robins, T. (1990) Cell Growth Diff. 1, 119-127). Here we present evidence that the receptor for GaLV (GLVR1) functions as a sodium-dependent transporter of inorganic phosphate. GLVR1 is shown to have approximately 3-4-fold higher affinity for phosphate than other mammalian phosphate transporters described to date. Productive infection of GLVR1-expressing cells by GaLV, but not other retroviruses, results in the complete blockade of GLVR1-specific uptake of inorganic phosphate. Since productive infection of cells with GaLV is generally not cytotoxic, it is likely that more than one phosphate transporter exists on the cell surface. Our data suggest that GLVR1 represents a sodium-dependent phosphate transporter that differs from other mammalian phosphate transporters in structure, affinity for phosphate, and function.