Pancreatic glucagon, the hyperglycemic hormone secreted by the alpha cells of the islets of Langerhans, promotes glycogenolysis, neoglucogenesis, lipolysis, and ketogenesis. Several abnormalities of glucagon secretion have been described in diabetes mellitus. These include absolute or relative hyperglucagonemia, exaggerated response to a protein load, and insufficient response to hypoglycemia. Although glucagon's role in diabetes has been challenged, the bulk of the evidence suggests that while insufficiency of insulin is the major abnormality involved, inappropriately elevated glucagon levels contribute to worsening of hyperglycemia. It is suggested that lowering of glucagon levels will result in better control of diabetes. To some extent, this can be achieved by continuous infusion of insulin in insulin-dependent diabetics. In addition, development of analogs of somatostatin holds promise of therapeutic benefit in both insulin-dependent and non-insulin-dependent types of the disease.