Peripheral blood lymphocytes from patients with uterine cervical cancer were tested against a cervical cancer cell line by micro-cytotoxicity assay. In stage O, high degree of cytotoxicity was observed but it decreased with progression of disease. In stage IV and recurrent cases, cytotoxic activity was negligible. Lymphocytes from healthy controls and myoma patients were not cytotoxic against target cells. On the other hand, lymphocyte response of phytohemagglutinin as a nonspecific T-cell activity was as high as the of healthy control in stage O, but the response decreased in stages I to IV and recurrent cases. In stages I to III, several cases showed cytotoxic activity but decreased response to phytohemagglutinin.