This invention provides novel peptides that function in vivo as agonists of the VPAC2 receptor. These insulin secretagogue polypeptides are shown to lower blood glucose in vivo more than controls upon glucose challenge. The polypeptides of this invention are also stable in formulation and have long half-lives. The peptides of the present invention provide a new therapy for patients with decreased endogenous insulin secretion, in particular type 2 diabetics. In particular, the invention is a polypeptide selected from a specific group of VPAC2-related polypeptides, or functional equivalents thereof. The invention is also directed to a method of treating a metabolic disease in a mammal comprising administering a therapeutically effective amount of the insulin secretagogue peptides to said mammal. Also disclosed are methods of making the peptides, both recombinant and synthetic.