Lymphokine-activated killer (LAK) cells can be generated by incubating fresh peripheral blood lymphocytes (PBL) in Interleukin-2 (IL-2). LAK cells kill fresh autologous and allogeneic human tumor cells in vitro. This study analyzes aspects of LAK cells that make them a promising candidate for the adoptive immunotherapy of human cancer. LAK cells can be generated from PBL of normal individuals and tumor-bearing patients. Pure, recombinant IL-2 generates LAK cells capable of killing a wide variety of tumors including sarcomas and cancers of the colon, pancreas, adrenal gland, and esophagus. Thirty-six of 41 (88%) fresh, noncultured, human tumor cell suspensions prepared from surgical specimens were lysed by LAK cells in a standard 4-hour chromium-release assay. Normal PBL were not killed. LAK cells can be expanded in vitro for periods longer than 2 months, potentially more than 10(20)-fold, while maintaining lytic ability. These results and the demonstrated efficacy of LAK cells in the therapy of murine tumors make LAK cells a candidate for clinical use in the adoptive immunotherapy of human cancer.