Since its discovery as a T-cell growth factor, interleukin 2 (IL-2) has attracted considerable scientific attention, not only as a useful reagent for the maintenance of large numbers of effector T lymphocytes but as a potentially potent immunoregulatory molecule, which could be of therapeutic usefulness in a number of clinical conditions. Outlined in this communication is a summary of the more salient biochemical features of murine and human IL-2, as well as the results of initial molecular biology experimentation aimed at the eventual production of IL-2 by recombinant DNA methodologies. These studies, together with those detailing the in vivo effectiveness of IL-2 therapy in a number of murine model situations, provide a current glimpse of future IL-2 aims and directions.