AbstractCultures of peritoneal exudate T lymphocyte‐enriched cells (PETLEC) fromListeria monocytogenes‐immune mice, antigen‐presenting cells (APC) and heat‐killedL. monocytogenesproduced high amounts of interferon‐γ (IFN‐γ). High IFN titers were also observed after stimulation ofL. monocytogenes‐immune cell cultures with the T cell mitogens concanavalin A and phytohemagglutinin.L. monocytogenes‐immune PETLEC produced several fold higher IFN titers than normal cell cultures in response to mitogen and antigen. Under both circumstances, APC were required for optimum responses.L. monocytogenes‐immune PETLEC participating in IFN production were Lyt 1+23−. IFN‐γ was also produced in cultures of clonedL. monocytogenes‐specific T cells. Since the same T cell clone showed antigen‐specific proliferative responses and interleukin productionin vitro, and could adoptively mediate delayed‐type hypersensitivity and anti‐listerial protectionin vivo, it is suggested that IFN production is a function of specific T cells active in