A B cell hybridoma (Désiré-1) was derived which secreted and expressed at its cell surface immunoglobulin (Ig) specific for the antigen-specific T cell receptor (Ti) of an H-2Kb-specific alloreactive cytotoxic T lymphocyte (CTL) clone (KB5-C20). It was found that the CTL clone could lyse hybridoma Désiré-1, whereas it could not lyse hybridoma which expressed surface Ig (sIg) binding to other cell surface structures of clone KB5-C20 such as the H-2Kk molecule. Blocking of CTL-target cell interactions using monoclonal antibodies (mAb) indicated that the CTL-target cell interaction was inhibited with appropriate anti-H-2 mAb and by anti-Lyt-2 mAb when CTL-H-2Kb interaction was involved but not when CTL-sIg interaction was involved. The two types of interactions were inhibited by anti-LFA-1 mAb. The involvement of the CTL-Ti structure was necessary to obtain a lytic interaction between CTL and target cells, but a major histocompatibility complex product on the target cells did not need to be involved. Comparison of CTL-target cell inhibition with cold target cells or with anti-clonotypic mAb indicated that the Ti-sIg cellular interaction was of much higher apparent affinity than the Ti-H-2Kb cellular interaction. These results further suggest potential regulatory effects of CTL-B cell cross-idiotypic interactions.