Peritoneal exudate lymphocytes from immune guinea pigs that bind in vitro to autologous antigen-pulsed macrophages were allowed to proliferate for 1 week to give a population markedly enriched in antigen-specific T cells. This enriched population was then studied with regard to its binding to fresh autologous antigen-pulsed macrophages. Specific binding was not inhibited by a large excess of antigen in the media (5000-fold greater than the amount of antigen associated with the macrophages) either soluble or bound to Sepharose beads, or by coating the antigen-pulsed macrophags with antibody to the exogenous antigen, by reacting a second layer of antibody to the heterologous antibody, or by haptenating the antigen and treating the hapten-antigen macrophage complex with excess anti-hapten antibody. Results of treating antigen-pulsed macrophages with the proteolytic enzymes trypsin and pronase indicate that exogenous antigen is on the macrophage surface, but the experiments failed to prove that the removable antigen is essential for binding. The simplest interpretation of these results is that the T cell receptor is not specific for native exogenous antigen.