Abstract: Methods for treating impaired glucose tolerance and early and late stage diabetes in mammals, for prophylactically sparing ?-cell function, aiding in preventing ?-cell death, preventing the onset of overt diabetes in a mammal with type 2 diabetes, treating the current level of glycemic control dysfunction of a mammal with impaired glucose tolerance or diabetes, comprising orally administering insulin and a delivery agent that facilitates insulin absorption from the gastrointestinal tract at the time of or shortly before mealtime, e.g., within about 10 minutes prior to ingestion of a meal, on a chronic basis. The methods also comprise, in addition to administering a rapid-acting insulin to provide a first insulin peak, administering a slow acting insulin to provide a second insulin peak occurring at a later time but of a longer duration.