Age‐dependent changes in natural killer (NK) cell activity was studied using the K 562 cell line as target in a 20 h51Cr release assay. Fifteen healthy, high‐aged persons (76–93 yrs) were compared with 15 sex‐matched young adults (20–39 yrs). Peripheral blood lymphocytes from one aged and one young person were assayed simultaneously; and in 12 of the pairs the elderly person expressed the highest cytotoxicity (p = 0.008). When the NK cell activity was expressed as lytic units per ml of blood, however, no difference could be found between the two age groups. T enriched cells showed lower NK activity than peripheral blood lymphocytes, but the age‐dependent changes were the same. The NK cell activity was positively correlated to the proportion of lymphocytes bearing receptors for the Fc part of IgG. The numbers of both Fc receptor positive peripheral lymphocytes and Fc receptor positive T cells (Tγcells) were significantly elevated in