Methods for use of an exendin, an exendin agonist, or a modified exendin or exendin agonist having an exendin or exendin agonist linked to one or more polyethylene glycol polymers, for example, for lowering glucagon levels and/or suppressing glucagon secretion in a subject are provided. These methods are are useful in treating hyperglucagonemia and other conditions that would be benefited by lowering plasma glucgon or suppressing glucagon secretion.