In all diabetic animal models studied to date, microangiopathic complications develop which can be prevented by tight control and reversed by either islet cell transplantation or transplanting the diabetic kidney into a nondiabetic environment. In humans the prevalence of these complications in secondary diabetes mellitus is similar to the prevalence in genetic diabetes. Furthermore, mesangial basement membrane thickness is normal at the onset of the disease and increases shortly thereafter. These two facts strongly suggest that the microangiopathic complications are not an independent genetic component but rather are secondary to the metabolic derangements of uncontrolled diabetes. Normal kidneys transplanted into diabetic recipients developed the vascular lesions of diabetes. Conversely, two diabetic kidneys inadvertently transplanted into nondiabetic recipients showed clearing of the vascular lesions.Most retrospective studies support the conclusion that control is associated with lessened complications. The three prospective studies published to date also support this hypothesis. Because glucose concentrations cannot be brought to normal levels by present methods, the critical question is whether a major emphasis on restoring metabolism to as nearly normal as possible will help ameliorate the microangiopathic complications in our patients. The accumulated evidence would strongly favor an affirmative answer. Two daily injections of intermediate-acting insulin supplemented with small amounts of short-acting insulin as needed is one method to approach this goal.