The role of Ag in the recruitment and localization of naive, acutely activated, and memory CD8+ T cells to the lung during influenza infection was explored using TCR-transgenic (Tg) mice. Naive, Thy1. 2+ CD8+ OT-I TCR-Tg cells were primed and recruited to the lung after transfer into congenic Thy1. 1+ recipients challenged with a genetically engineered influenza virus (influenza A/WSN/33 (WSN)-OVA I) containing the K b restricted OVA 257–264 epitope (siinfekl) in the viral neuraminidase stalk. However, if the transferred animals were infected with a similar influenza virus that expressed an irrelevant K b epitope (WSN-PEPII), no TCR-Tg T cells were detectable in the lung, although they were easily visible in the lymphoid organs. Conversely, there were substantial numbers of OT-I cells found in the lungs of WSN-PEPII-infected mice when the animals had been previously, or were concurrently, infected with a recombinant vaccinia virus expressing OVA. Similar results were obtained with nontransgenic populations of memory CD8+ T cells reactive to a murine γ-herpesvirus-68 Ag. Interestingly, the primary host response to the immunodominant influenza nucleoprotein epitope was not affected by the presence of memory or recently activated OT-I T cells. Thus, although Ag is required to activate the T cells, the subsequent localization of T cells to the lung during a virus infection is a property of recently activated and memory T cells and is not necessarily driven by Ag in the lung.