Malignant pleural mesothelioma is refractory to conventional therapy. We tried local adoptive immunotherapy using lymphokine-activated killer (LAK) cells and interleukin-2 (IL-2) to control malignant pleural effusion due to mesothelioma in two patients: Case 1 was that of a 69-year-old man, and Case 2 that of a 49-year-old woman with complicating chronic idiopathic thrombocytopenic purpura. A systemic survey revealed no sign of metastasis in either case. Intrapleural instillations of 6.7 x 10(9) autologous LAK cells in Case 1, or 11.3 x 10(9) allogeneic LAK cells in Case 2, with daily injections of IL-2 resulted in reductions of the pleural effusions in each case and in a decline in the level of hyaluronic acid in the effusion, in Case 1. The instillations of autologous and allogeneic LAK cells were well tolerated. The results suggest that local adoptive immunotherapy could be useful in the treatment of malignant effusion due to mesothelioma.