Peripheral blood lymphocytes obtained from patients by leukapheresis were cultured in RPMI 1640 containing human plasma and interleukin 2. The morphology, phenotypes and cytotoxicity of induced LAK cells were studied. Lymphoblastoid cells mainly proliferated were OKIa1+ cells and were thought to be LAK cells. Maximal cytotoxicity was obtained after two weeks of incubation. IL-2 enhanced the cytotoxicity of LAK cells. Autologous LAK cells induced by two weeks of incubation were injected into patients. One case of pulmonary metastases of breast cancer showed reduction and two lesions showed partial regression. Also, no new lesions appeared in the lungs of a patient with alveolar soft-part sarcoma.