The studies discussed here show two distinct roles for glucagon in the treatment of diabetes. Glucagon may have a direct role in the pa- thogenesis of diabetes, with a relative hyperglucagonaemia in all forms of diabetes. It is not clear if this is a consequence or a cause of diabetes, nor whether harmful or a possible endogenous counter-regulation me- chanism to compensate for some adverse metabolic change. Antagonising glucagon action may reduce the associated hypergly- caemia, but may not be beneficial in terms of life expectation of the person with diabetes. One of the main causes of type 2 diabetes is obesity. Glucagon can cause significant weight loss through reducing food intake and increasing energy expenditure; and if this reduces obesity, could itself treat diabetes. To mitigate any hyperglycaemic effects of the glucagon, it will, however, have to be administered with another hormone such as GLP-1 which releases insulin and thereby inhibits the enhanced gluconeogenesis of glucagon.