We have described the use of a cloned murine IL-2-dependent T-cell line to directly measure feline IL-2. Concanavalin A stimulated feline peripheral blood lymphocytes produced an IL-2-rich supernatant that supported the growth of this murine IL-2-dependent T-cell line. In addition to producing IL-2, Con A stimulated killer cells in PBL were cytotoxic for the FeLV transformed tumor cell line FL74. Incubating feline PBL with a cocktail of the calcium ionophore A23187 and phorbol ester also led to the generation of cytotoxic cells as well as the production of high levels of IL-2. Finally, IL-2-rich supernatant was able to stimulate cytotoxic activity in PBL from normal cats.