Seventeen consecutive s.c. murine tumors, derived from a sarcoma and a colon adenocarcinoma, were cultured in the presence of recombinant interleukin 2 (rIL-2) for growth of tumor-infiltrating lymphocytes (TIL). Identical cultures were activated by solid-phase monoclonal antibody directed against the murine CD3 epsilon-chain, in conjunction with rIL-2. Forty-eight h later, cells were replaced in rIL-2 alone. Proliferation of anti-CD3-stimulated cultures was 1- to 17-fold greater than those cultured with rIL-2 alone (P less than 0.05). Both culture conditions yielded TIL which stained greater than 80% Thy-1.2+/Lyt-2+ (P greater than 0.05), less than 7% Thy-1.2+/L3T4+ (P greater than 0.05). Regardless of culture condition, longitudinal studies of in vitro cytotoxicity generated from 10 TIL preparations revealed no significant differences between the ability of TIL to lyse the murine natural killer-sensitive line YAC or heterologous or autologous tumor (P greater than 0.05). In vivo antitumor activity of TIL was tested by the adoptive transfer of suboptimal doses of TIL plus systemic rIL-2 to mice with pulmonary micrometastatic disease. No difference in tumor regression was noted between the TIL cultured with anti-CD3 plus rIL-2 or with rIL-2 alone (P greater than 0.05). Anti-CD3 stimulation of murine TIL cultures significantly increases lymphocyte cell yield without alteration of their phenotype, in vitro tumoricidal activity, or in vivo therapeutic effect.