We have isolated and partially sequenced a M(r) 160,000 glycoprotein whose rate of cycling to and from the adipocyte cell surface is enhanced by insulin in a manner apparently identical to the effect of insulin on GLUT4 cycling. Based on the protein sequence, we have prepared an antipeptide antibody against this protein, gp160. The antibody recognizes a M(r) 160,000 protein whose subcellular distribution is identical to that of GLUT4. This was determined by three separate criteria: (i) Western blotting of fractionated adipocyte membranes from cells exposed to insulin or not, (ii) adsorption of vesicles with anti-GLUT4 antibodies followed by Western blotting, and (iii) separation of microsomal vesicles by sucrose velocity and density gradients. By all three criteria, GLUT4 and gp160 are completely colocalized in rat fat cells. Moreover, gp160 can be detected by Western blot only in fat and cardiac and skeletal muscles and was absent from all other tissues tested. Thus, gp160 is an additional marker for physiologically important, insulin-sensitive glucose transport. Its further study at the protein and DNA level may reveal information about the mechanistic details of insulin-activated GLUT4 translocation as well as information concerning the tissue-specific expression of GLUT4 and gp160.