Using Epstein-Barr virus B cell clones and antigen-specific T cell clones, we asked how antigen-antibody complexes are handled by B cells. We found that the only B cells capable of efficient presentation of antigen-antibody complexes are those that bind the complexes via membrane immunoglobulin, i.e., rheumatoid factor-producing B cells and, to a lower extent, antigen-specific B cells. On the contrary, nonspecific B cells, although capable of binding antigen-antibody complexes, fail to present them to T cells. Thus, rheumatoid factor B cells can present any antigen in the context of an immune complex and be triggered by T cells specific for a variety of foreign antigens. These results demonstrate a mechanism of intermolecular help that may be responsible for the production of rheumatoid factor and possibly of other types of autoantibodies.