The effect of streptozotocin (STZ) on the glucose transporter 2 (GLUT2) expression in beta-cells was investigated in vitro and in vivo. By Western blot analysis, a gradually decreasing GLUT2 expression was found in islets prepared from C57BL/6 male mice that had received multiple low doses of STZ (MD-STZ) for induction of autoimmune diabetes. Reduction of GLUT2 expression correlated with the number of STZ injections administered and preceded development of hyperglycemia. When hyperglycemia had developed, GLUT2 expression was extremely reduced. In vitro, incubation of isolated islets with STZ resulted in a time- and dose-dependent reduction of beta-cell GLUT2 expression. In vivo, pretreatment of MD-STZ recipients with intraperitoneal injections with 5-thio-D-glucose (5-T-G) just before each of the STZ injections prevented MD-STZ-induced beta-cell GLUT2 reduction and hyperglycemia development. In vitro, preincubation of islet cultures with 5-T-G also prevented STZ-induced GLUT2 reduction. Unlike STZ, equimolar concentrations of methylnitrosourea (MNU), the aglycone moiety of STZ, failed to alter GLUT2 expression in vitro. In conclusion, our data demonstrate that STZ-induced beta-cell GLUT2 reduction was prevented by 5-T-G both in vitro and in vivo in the MD-STZ diabetes model. The noxious effect of STZ on GLUT2 expression is most likely facilitated through its glucose moiety, because MNU lacked to do so. Presumably, in autoimmune MD-STZ diabetes the GLUT2 glucose transporter might be a key target structure for STZ subtoxicity and diabetogenicity, which converge with subsequent immune reactions to beta-cell destruction.