To induce hyperglycemia in mice by administration of STZ, two experimental protocols that involve different pathogenic pathways are being used. First, the intraperitoneal injection of a single high dose (HD-STZ) exerts direct toxicity on β-cells, which results in necrosis within 48–72 h and overt permanent hyperglycemia. Second, injections of multiple low doses of STZ (LD-STZ), administered intraperitoneally on 5 consecutive days, induce both β-cytotoxic effects and STZ-specific T-cell-dependent immune reactions. In LD-STZ models, only a combination of toxic and immunological effects result in gradually increasing hyperglycemia, provided male mice of susceptible strains are being used. In this study, we found that 5-T-G, a glucose analogue that has sulfur for oxygen in the pyranose ring, prevented, in a dose-dependent way, both HD-STZ- and LD-STZ-induced hyperglycemia and that D-G, which was only tested in the LD-STZ system, was also protective, albeit somewhat less so than 5-T-G. This protective effect was achieved by intraperitoneally injecting 5-T-G and D-G, respectively, right before each STZ injection. Protection against hyperglycemia was already achieved with a total of 3 injections of 5-T-G, 1 injection each given before the first 3 of 5 LD-STZ injections. By means of OGTT, it was determined that pretreatment with 5-T-G afforded protection from substantial β-cell damage in vivo. In addition, significant (P < 0.005) in vitro β-cell protection with 5-T-G was documented by assaying for basal and glucose-stimulated IRI release in bulk cultures of islets, isolated from LD-STZ-injected and 5-T-G-pretreated donors. Interestingly, pretreatment with 5-T-G failed to prevent STZ-induced inflammatory reactions, as assessed by two different methods. First, by PLN assay, it was shown that the T-cell-dependent immune reactions to STZ as antigen were not affected by pretreatment with 5-T-G. Second, histological examinations indicated that the mononuclear cell infiltrates of pancreatic islets were not changed by pretreatment with 5-T-G. In conclusion, our data indicate that 5-T-G and D-G protected against hyperglycemia by preventing the β-cell toxic effects of STZ, not by preventing its inflammatory effect in the LD-STZ model.