For many patients with type 2 diabetes mellitus, metformin plus appropriate treatment for cardiovascular risk factors form the cornerstone of drug therapy.1 However, the progressive impairment of both the secretion and action of insulin in the condition mean that high blood glucose concentrations usually worsen over time, so necessitating escalation of hypoglycaemic therapy. Three drugs in two new classes that act on the hormonal regulation of insulin secretion have been launched recently for use as add-in therapies in patients with type 2 diabetes: exenatide (Byetta--Eli Lilly), sitagliptin (Januvia--MSD), and vildagliptin (Galvus--Novartis). Here we consider whether they have a role in the management of such individuals.