Most mammalian cells take up glucose by passive transport proteins in the plasma membranes. The best known of these proteins is the human erythrocyte glucose transporter, GLUT1. High levels of heterologous expression far the transporter are necessary for the investigation of its three-dimensional structure by crystallization. To achieve this, the baculovirus expression system has become popular choice. However, Spodoptera frugiperda Clone 9 (Sf9) cells, which are commonly employed as the host permissive cell line to support baculovirus replication and protein synthesis, grow well on TC-100 medium that contains 0.1% D-glucose as the major carbon source, suggesting the presence of endogenous glucose transporters. Furthermore, very little is known of the endogenous transporters properties of Sf9 cells. Therefore, human GLUT1 antibodies would play an important role for characterization of the GLUT1 expressed in insect cell. However, the successful use of such antibodies for characterization of GLUT1 expression m insect cells relies upon their specificity for the human protein and lack of cross-reaction with endogenous transporters. It is therefore important to determine the potential cross-reactivity of the antibodies with the endogenous insect cell glucose transporters. In the present study, the potential cross-reactivity of the human GLUT1 antibodies with the endogenous insect cell glucose transporters was examined by Western blotting. Neither the antibodies against intact GLUT1 nor those against the C-terminus labelled any band migrating in the region expected fur a protein of M$_r$ comparable to GLUT1, whereas these antibodies specifically recognized the human GLUT1. Specificity of the human GLUT1 antibodies tested was also shown by cross-reaction with the GLUT1 expressed in insect cells. In addition, the insect cell glucose transporter was found to have very low affinity for cytochalasin B, a potent inhibitor of human erythrocyte glucose transporter.