In wild-type mice, a single injection of streptozotocin (STZ, 200 mg/kg body wt) caused within 4 days severe hyperglycemia, hypoinsulinemia, significant glucose intolerance, loss of body weight, and the disappearance of pancreatic β-cells. However, in ATP-sensitive K+channel (KATPchannel)-deficient mice (Kir6.2−/−mice), STZ had none of these effects. Exposing isolated pancreatic islets to STZ caused severe damage in wild-type but not in Kir6.2−/−islets. Following a single injection, plasma STZ levels were slightly less in Kir6.2−/−mice than in wild-type mice. Despite the difference in plasma STZ, wild-type and Kir6.2−/−liver accumulated the same amount of STZ, whereas Kir6.2−/−pancreas accumulated 4.1-fold less STZ than wild-type pancreas. Kir6.2−/−isolated pancreatic islets also transported less glucose than wild-type ones. Quantification of glucose transporter 2 (GLUT2) protein content by Western blot using an antibody with an epitope in the extracellular loop showed no significant difference in GLUT2 content between wild-type and Kir6.2−/−pancreatic islets. However, visualization by immunofluorescence with the same antibody gave rise to 32% less fluorescence in Kir6.2−/−pancreatic islets. The fluorescence intensity using another antibody, with an epitope in the COOH terminus, was 5.6 times less in Kir6.2−/−than in wild-type pancreatic islets. We conclude that 1) Kir6.2−/−mice are STZ resistant because of a decrease in STZ transport by GLUT2 in pancreatic β-cells and 2) the decreased transport is due to a downregulation of GLUT2 activity involving an effect at the COOH terminus.