The inhibition of Phosphatidylinositol 3-kinase (PI-3K) disrupts the ability of insulin to stimulate GLUT1 and 4 translocation into the cell membrane. The effect on GLUT4 but not on GLUT1 is mediated by activation of PKB. The serum and glucocorticoid inducible kinase SGK1, a further kinase downstream of PI-3K, regulates several transporters. GLUT1 contains a SGK1consensus site at serine 95. Thus, the present study investigated whether GLUT1 is regulated by the kinase. Tracer-flux studies in Xenopus oocytes and mammalian cells demonstrated that GLUT1-mediated glucose transport is enhanced by constitutively active S422DSGK1. The effect requires the kinase catalytical activity since the inactive mutant K127NSGK1 failed to modulate the transporter. GLUT1 stimulation by S422DSGK1 is not due to de novo protein synthesis but rather to an increase of the transporter protein abundance in the plasma membrane. Kinetic analysis revealed that SGK1 enhances maximal transport rate without altering GLUT1 substrate affinity. Tracer flux studies in adipocytes isolated from SGK1 wild type and knockout mice demonstrated the role of SGK1 in glucose transport regulation. These observations suggest that SGK1 modulates GLUT1 and may contribute to or account for the PI-3K dependent stimulation of GLUT1 by insulin.