Back ground & Aim of the work: Diabetes mellitus (DM) is a chronic metabolic disorder brings great danger to human health. Low-dose-rate radiation modulates various biological responses including carcinogenesis, immunological responses and diabetes. This study  examined the effect of low doses of irradiation on the pathological and ultrastructural  progression of type I diabetes in rats inducted by Streptozotocin.
Material and Methods: The present study was done on 80 healthy adult albino male rats 9 weeks age, in the weight range from (150–200 gm). Rats were grouped to 4 groups they were cared  according to the Guiding Principle in the Care and Use of Animals. Diabetes was induced by a single intraperitoneal injection of freshly prepared Streptozotocin (STZ- 45 mg/kg b.w.).
Whole body gamma irradiation was performed using Caesium -137. Animals were exposed to fractionated dose levels of 0.5 Gy/week of γ-radiation for 3 and 6 weeks. The body weight, blood glucose and insulin levels were measured after 3 and 6 weeks. Small blocks of pancreatic tissues  of different groups were removed and prepared for  pathological and ultrastructure examination.
 Results: An elevated level of glucose and decreased level of insulin in blood were first detected at 3 and 6 weeks of age in the STZ treated rats. There was significant and remarkable tendency of  gaining normal levels of both blood glucose and blood insulin by irradiation exposure especially after 6 weeks of irradiation.  Both suppression of cell death and cellular injury induced by STZ were also observed by EM examination in 3 week  and 6 weeks.
Conclusion: The present results indicated that treatment with 0.5 Gy γ rays suppresses progression of type I diabetes in STZ rats.