Adoptive transfer of antigen-specific cytotoxic T lymphocytes (CTLs) has been successfully used to treat patients with different types of cancer. However, the long-term spatial-temporal dynamics of the distribution of systemically infused CTLs remains largely unknown. Noninvasive imaging of adoptively transferred CTLs using molecular-genetic reporter imaging with positron emission tomography and computed tomography (PET-CT) represents an innovative approach to understanding the long-term migratory patterns and therapeutic potential of adoptively transferred T cells. Here we report the application of repetitive PET-CT imaging with [18F]fluoro-5-ethyl-1-beta-D-arabinofuranosyluracil (18F-FEAU) in two nonhuman primates demonstrating that autologous polyclonal macaque T lymphocytes activated and transduced with a retroviral vector encoding for the sr39 mutant herpes simplex virus 1 thymidine kinase (sr39HSV1-tk) reporter gene can be detected after intravenous infusion in discrete lymphoid organs and in sites of inflammation. This study represents a proof of principle and supports the application of 18F-FEAU PET-CT imaging for monitoring the distribution of intravenously administered sr39HSV1-tk gene-transduced CTLs in humans.