Recently developed procedures for the isolation and continuous growth in vitro of T lymphocytes can be used to extend our knowledge of cellular immune responses elicited by parasitic infections. These procedures are adaptable to the study of both the inductive and effector phases of T cell responses. The inductive phase of T cell responses is measured by assessing the level of blastogenesis induced in antigen-primed lymphocyte populations by parasite antigens. The development of limiting dilution analyses and procedures for the repeated in vitro restimulation of such cells have allowed for the quantitation of blastogenic responses, and for the isolation of antigen-reactive T cells. The effector phase of T cell responses is assessed by assays that detect either, cytolytic activity of the antigen-responsive cells, the secretion of lymphokines by the responding cells, or specific or non-specific T cell mediated immunosuppression.