The virus-specific CD8⁺ T cell response has been analyzed through the development, effector, and recovery phases of primary and secondary influenza pneumonia. Apparently, most, if not all, memory T cells expressing clonotypic receptors that bind a tetrameric complex of influenza nucleoprotein (NP)_366–374 peptide+H-2D^b (NPP) are induced to divide during the course of this localized respiratory infection. The replicative phase of the recall response ends about the time that virus can no longer be recovered from the lung, whereas some primary CD8⁺NPP⁺ T cells may proliferate for a few more days. The greatly expanded population of CD8⁺NPP⁺ memory T cells in the lymphoid tissue of secondarily challenged mice declines progressively in mean prevalence over the ensuing 100 days, despite the fact that at least some of these lymphocytes continue to cycle. The recall of cell-mediated immunity thus is characterized by massive proliferation of the antigen-specific CD8⁺ set, whereas the extent of lymphocyte turnover in the absence of cognate peptide is variable, at a low level, and can be influenced by intercurrent infection.