The gIII glycoprotein of bovid herpesvirus 1 (BHV-1) has been shown to mediate the adsorption of the virions to cells (K. Okazaki, E. Honda, T. Minetoma, and T. Kumagai, 1987, Arch. Virol. 97, 297-307). In this study, the cellular receptor for BHV-1 was investigated. Addition of heparin to the virus inoculum and treatment of the cells with heparinase prevented the virus from adsorbing to and infecting the cells. Of the major glycoproteins of BHV-1 only gIII was found to bind specifically to heparin. The binding of gIII was inhibited by a monoclonal antibody against antigenic site Ia, which interferes with the adsorption of the virus. These findings indicate that the virus adsorption to cells is mediated by interaction of the gIII antigenic site Ia with a heparinlike moiety on the cell surface, which serves as a receptor for BHV-1.