Highly purified human blood lymphocytes which had been incubated with antibody-complexed chicken erythrocytes, adsorbed 50 to 100 × more of this antibody (rabbit) than lymphocytes incubated with antibody-IgG without erythrocytes. Most of the adsorbed IgG was present in the form of antigen-antibody complexes, derived from lysed erythrocytes and not removable from the lymphocytes by repeated washing. When tested in subsequent cytotoxicity tests, the lymphocytes which carried antigen-antibody complexes were specifically cytotoxic for freshly added chicken erythrocytes. This was not the case with lymphocytes preincubated with antibody-IgG alone, with antibody IgG and noncross-reactive duck erythrocytes, or with IgG from normal rabbit serum. The results indicate that some lymphocytes have high affinity for antigen-antibody complexes. Antibody taken up in this way may be reutilized, thereby conferring specific effector functions on a population of normal lymphocytes. When complex-carrying lymphocytes were incubated with fresh erythrocytes and small amounts of fresh anti-erythrocyte antibody, however, they were less cytotoxic than those preincubated with antibody alone or with normal rabbit IgG. This may at least in part reflect a competition for lymphocytic sites with affinity for immunoglobulin and may be necessary for triggering of the antibody-induced cytotoxicity of lymphocytes.