Tumor-infiltrating lymphocytes (TILs) are host T cells that can be grown from fresh murine and human tumors using interleukin-2 (IL-2) in bulk cultures. These activated T cells have been shown to have significant antitumor activity both in vitro and in vivo. A technique is described for the separation of Thy-1.2-positive TILs from fresh murine tumors using antibody-coated magnetic beads, permitting the examination of growth conditions for these cells. TILs with increased therapeutic efficacy are obtained from the immunogenic MCA 38 and MCA 105 tumors when culture conditions employing low levels of IL-2 (10 vs. 1,000 U/ml) and irradiated autologous tumor restimulation are used. TILs grown under these conditions can mediate a 93% reduction of 3-day-old established pulmonary metastases when as few as 2.5 x 10(5) cells are adoptively transferred with systemic IL-2. These culture conditions are utilized to grow TILs from the nonimmunogenic MCA 102 tumor for which bulk TIL culture methods are unsuccessful. MCA 102 TILs grown in this fashion demonstrate in vivo therapeutic efficacy against established autologous pulmonary metastases.