AbstractTo eliminate the role of natural killer (NK), antibody‐dependent cell‐mediated cytotoxicity (ADCC), and polymorphonuclear leukocyte (PMN)‐mediated cytotoxicity in Varicella zoster virus (VZV) infections, peripheral blood mononuclear cell (PBMC)‐mediated NK and ADCC, and phorbol myristate acetate‐stimulated PMN‐mediated cytotoxicity against VZV‐infected targets were studied in children with leukemia.Natural killer and PMN‐mediated cytotoxic activity was depressed for 6 months after complete remission and ADCC activity was depressed for 1 year after complete remission. The magnitude of three cytotoxic mechanisms in leukemic children gradually increased while they continued in complete remission.These results suggested that decreased cytotoxic activities of PBMC and PMN might contribute to serious VZV infections and susceptibility to herpes zoster in le