OBJECTIVES: The authors discuss upon the changes in the two cell types involved in cell mediated immunity (Killer and Natural Killer) as a result of operation in malignant ovarian tumor atients. METHODS: They study the preoperative and postoperative cell mediated immunity of 28 malignant cystadenocarcinoma cases (FIGO stage I/a-III/c). To determine the maximum K and NK cell activity they used the kinetic model of cytotoxicity enzyme. RESULTS AND CONCLUSIONS: They conclude that operation of malignant ovarian tumors had no significant influence on K and NK cell activity. They hypothesize that unchanged cell mediated immunity seems to be independent of malignant tumors, especially in these conditions. We need further information about this change of cell mediated immunity.