AbstractUsing unstimulated rat peritoneal cells as immunogen a new monoclonal antibody KiM4R was produced. Ki‐M4R recognizes follicular dendritic cells (dendritic reticulum cells) in germinal centers of lymphoid follicles in lymphatic tissue. In addition, sinus lining cells, endothelia of postcapillary venules, as well as mesangial cells of the renal glomerula immunoreact with Ki‐M4R in vitro as well as in vivo. This antibody might be useful for studying the interaction of follicular dendritic cells and B‐cell immune response.