In malignant pleural effusion, lymphocytes (MPEL) and autologous tumor cells (ATC) were obtained by centrifugation on discontinuous density gradients from 16 patients with malignant pleural effusion. The cytotoxicity of MPEL against ATC were compared with that of peripheral blood lymphocytes (PBL). It was demonstrated that the results for separation with 100%: 60% Ficoll-Hypaque which formed a discontinuous density gradients were the best in three sets of discontinuous density gradients. The cytotoxicity of PBL was higher than that of MPEL (P < 0.001), but the cytotoxicity and expansion of MPEL-activated by rIL2 was much higher than that of PBL-activated by rIL2 (LAK cells) (P < 0.001). This shows that local immune reaction within pleural cavity of patients with malignant pleural effusion was in the state of suppression, but the state could be improved by using rIL2. Therefore, we consider that MPEL could be the better effector cells than LAK cells in tumor adoptive immunotherapy.