Macrophages stimulated with a high dose of LPS were lysed by NK cells. IL-2–activated NK cells (ie, NK cells 1 day after restimulation with human recombinant IL-2), resting NK cells (ie, NK cells expanded with IL-2 but used 8 days after restimulation), or freshly isolated NK cells were tested for their cytolytic activity against autologous unstimulated macrophages or autologous macrophages incubated with 100 ng/mL (macrophage^{low LPS}) or 200 ng/mL (macrophage^{high LPS}) LPS for 48 hours. NK cells and target cells were incubated at the ratios indicated, and specific lysis was measured by a standard ³⁵S release assay. In each experiment the spontaneous release of ³⁵S was less than 20% of the total. The mean of at least 3 independent experiments using cells from different donors is shown.