Recent increases in knowledge of cellular immunology, combined with developments in biotechnology, have provided new opportunities for the development of immunotherapies for the treatment of cancer in humans. One approach to therapy is that of adoptive immunotherapy, that is, the transfer to the tumor bearing host of lymphoid cells with antitumor reactivity that can mediate antitumor responses. Several lymphocyte subpopulations have now been identified that may be suitable for use in adoptive immunotherapy. Resting lymphocytes incubated in interleukin-2 (IL-2) give rise to lymphokine activated killer (LAK) cells that can lyse malignant cells, but not normal cells. Clinical studies in patients with advanced cancer have revealed that treatment with high dose IL-2 alone or in combination with LAK cells can mediate the complete or partial regression of cancer in selected patients. Other approaches are currently undergoing investigation, including the adoptive transfer of tumor infiltrating lymphocytes, which, in animal models, have antitumor reactivity 50-100 times more potent than do LAK cells. Other new approaches to immunotherapy include the use of combination of lymphokines, such as the use of tumor necrosis factor or alpha interferon in conjunction with IL-2. The availability of recombinant lymphokines that provide large amounts of biologically active materials can hopefully lead to the development of effective new therapies for cancer in humans.