T cells are activated when the antigen‐specific T cell receptor recognizes antigen in association with major histocompatibility complex (MHC) proteins. The T cell surface protein CD2 (T11, LFA‐2, the T erythrocyte receptor) and its target or stimulator cell ligand, lymphocyte function‐associated antigen‐3 (LFA‐3), are also involved in T cell adhesion and activation. The molecular mechanisms by which the CD2/LFA‐3 interaction affects T cell adhesion and activation are unclear. The CD2/LFA‐3 interaction may be modeled by the interaction between LFA‐3 and anti‐LFA‐3 monoclonal antibody (mAb). We used the fluorescence photobleaching recovery technique to investigate the effect of anti‐LFA‐3 mAb on the lateral mobility of MHC proteins in plasma membranes of JY, a human Epstein‐Barr virus‐transformed B cell line. Anti‐LFA‐3 mAb induced immobilization of class I MHC proteins labeled with bivalent but not monovalent fluorescein‐conjugated W6/32 mAb. Anti‐LFA‐3 mAb also caused immobilization of class II MHC proteins labeled with bivalent fluoresceinated LB3.1 mAb. In contrast, anti‐LFA‐3 mAb did not affect the mobilities of either a B cell membrane protein labeled with bivalent fluoresceinated anti‐CD45 (human leukocyte antigen) mAb or a membrane lipid analogue. Unlike anti‐LFA‐3 mAb, anti‐LFA‐1 mAb did not affect class I MHC protein mobility. These results suggest that CD2 binding to LFA‐3 may trigger a physiological response in which target cell MHC proteins, cross‐linked by receptors on the T cell surface, are immobilized at and thereby localized to the T cell‐target cell interface.