Although T cells are required for acute lung rejection, other graft–infiltrating cells such as neutrophils accumulate in allografts and are also high glucose utilizers. Positron emission tomography (PET) with the glucose probe [18F]fluorodeoxyglucose ([18F]FDG) has been employed to image solid organ acute rejection, but the sources of glucose utilization remain undefined. Using a mouse model of orthotopic lung transplantation, we analyzed glucose probe uptake in the grafts of syngeneic and allogeneic recipients with or without immunosuppression treatment. Pulmonary microPET scans demonstrated significantly higher [18F]FDG uptake in rejecting allografts when compared to transplanted lungs of either immunosuppressed or syngeneic recipients. [18F]FDG uptake was also markedly attenuated following T cell depletion therapy in lung recipients with ongoing acute rejection. Flow cytometric analysis using the fluorescent deoxyglucose analog 2-NBDG revealed that T cells, and in particular CD8+ T cells, were the largest glucose utilizers in acutely rejecting lung grafts followed by neutrophils and antigen-presenting cells. These data indicate that imaging modalities tailored toward assessing T cell metabolism may be useful in identifying acute rejection in lung recipients.