The cellular uptake of glucose catalysed by the facilitated glucose transporter (GLUT) family is further regulated by metabolites and hormones, most importantly by insulin. All of the six isoforms known in this family possess a large cytoplasmic domain of divergent amino acid sequence. A body of evidence indicates that this domain is important for GLUT regulation. Exactly how this domain participates in the regulation, however, is not known. A likely possibility is that a specific cellular protein interacts with GLUT at this domain, and thus modulates the function. This putative, glucose transporter binding protein (GTBP) may be an enzyme, or a non-enzymic adaptor or docking protein. Indeed, we have identified several cellular proteins that bind to the cytoplasmic domain of GLUT proteins; these include glyceraldehyde-3-phosphate dehydrogenase, glucokinase, GTBP70, GTBP85, GTBP28 and L-3-hydroxyacyl-CoA dehydrogenase. Some of these GLUT-GTPB interactions are functionally coupled. Whether any of these interactions actually participates in the insulin-induced GLUT regulation is yet to be determined.