Abstract Objective: This study assessed the pharmacokinetics, pharmacodynamics, and tolerability of single doses of exenatide in adolescent patients with type 2 diabetes mellitus (T2DM). Methods: This was a randomized, single-blind, dose-escalation, crossover study in adolescent (age 10–16 years) patients with T2DM who were being treated with diet and exercise or a stable dose of metformin, a sulfonylurea, or a combination of metformin and a sulfonylurea for at least 3 months before screening. Eligible patients were allocated to receive single subcutaneous doses of exenatide 2.5 μg, exenatide 5 μg, and placebo, each followed by a standardized meal, on 3 separate days (maximum interval between first and third doses, 5 weeks). Exenatide 2.5 μg always preceded exenatide 5 μg in each treatment sequence. The primary end points were the pharmacokinetics and safety profile of exenatide; secondary end points included postprandial plasma glucose, serum insulin, and plasma glucagon concentrations. Results: The study enrolled 13 adolescent patients with T2DM (7 females, 6 males; mean SD age, 15 1 years; body mass index, 32.5 5.0 kg/m2 ; glycosylated hemoglobin, 8.2% 1.5%). After administration of exenatide 5 μg, the geometric mean (SE) exenatide AUC0−∞ and Cmax were 339.5 (39.6) pg · h/mL and 85.1 (11.5) pg/mL, respectively (n = 12). The exenatide AUC appeared to be dose dependent, although exenatide was not quantifiable in all patients at the 2.5-μg dose; after administration of exenatide 2.5-μg, the geometric mean AUC0−∞ ) was 159.2 (23.1) pg · h/mL (n = 6) and the geometric mean Cmax was 56.3 (10.1) pg/mL (n = 9). Both exenatide doses were associated with significant reductions in postprandial plasma glucose excursions compared with placebo ( P < 0.01); the incremental mean (SE) AUC15–360min was −3465.6 (1587.3) mg · min/dL for exenatide 2.5 pg, −4422.2 (2434.4) mg · min/dL for exenatide 5 μg, and 3457.4 (1615.5) mg · min/dL for placebo. The 2 exenatide doses were also associated with significant reductions in postprandial plasma glucagon concentrations compared with placebo ( P < 0.01); the respective incremental mean values for AUC15–180min were 125.5 (658.4), −1403.8 (632.1), and 1843.1 (540.6) pg · min/mL. There were no significant differences in serum insulin concentrations between exenatide and placebo. Exenatide was generally well tolerated, with no hypoglycemic events recorded during the study. Conclusions: In these adolescent patients with T2DM, administration of single 2.5- and 5-μg doses of exenatide were associated with dose-dependent increases in plasma exenatide concentrations and improved postprandial glucose concentrations compared with placebo. Both doses appeared to be well tolerated. ClinicalTrials.gov Identifier: NCT00254254.