The number of peripheral blood lymphocytes (PBL) rosetting with sheep erythrocytes (SE-rosettes) was significantly decreased by preincubation with both sera containing immune complexes (IC) and prepared antigen-antibody complexes. However, this effect of decrease in rosetting ability of PBL could be completely reversed by a second incubation of the cells for 30 minutes at 37 degrees C in IC-free medium. The immune complexes and antigen-antibody complexes respectively could bind reversibly to T cells via Fc-receptors and subsequently interfere with the T cell receptors for SE by steric hindrance.