dog diagnosed as insulinoma with concurrent peripheral polyneuropathy was treated with surgical resection and postoperative streptozotocin (STZ) therapy. Beginning on the 62nd postoperative day, intravenous administration of STZ (500mg/m2) was performed every three weeks. The dog's blood glucose level returned to the normal range and neurological signs improved after the administration of two doses of STZ. At the third administration of STZ, recurrent hypoglycemia was identified. The dog's condition did not improve and a seizure followed. The dog was euthanatized due to the development of the hypoglycemic seizure on the 127th postoperative day. Normoglycemia had been maintained without severe side effects, such as renal dysfunction, f or two months after the operation. We therefore suggest that STZ therapy is useful in the medical management of canine insulinoma.