This mechanistic study will evaluate the effect of vildagliptin on glucose-stimulated insulin secretion to improve the incretin effect in patients with type 2 diabetes.

Inclusion Criteria:

• Patients with type 2 diabetes on metformin for at least 3 months and have been on a stable dose of at least 1500 mg daily for a minimum of 4 weeks
• Agreement to maintain the same dose of metformin throughout the study
• Body mass index (BMI) in the range of 22-35 kg/m2
• HbA1c in the range of 7.0 to 9.0%
• FPG <200 mg/dl (11.1 mmol/L)
• Agreement to maintain prior diet and exercise habits during the full course of the study
• Ability to comply with all study requirements and signed informed consent to participate in the study

Exclusion Criteria:

• A history of type 1 diabetes
• A history of acute metabolic diabetic complications
• Evidence of significant diabetic complications
• Insulin treatment for longer than 10 days within the past 6 months
• Treatment with any oral anti-diabetic other than metformin within 3 months prior to visit 1

Other protocol-defined inclusion/exclusion criteria may apply