We coupled a monoclonal anti-human IgD to the gp350 gylcoprotein of Epstein-Barr virus, which has been shown to bind to the complement receptor 2 (CR2), and compared its B cell stimulatory ability to that of anti-Ig and to a multivalent anti-Ig-dextran conjugate. The anti-Ig-gp350 conjugate stimulated higher levels of human B cell proliferation in vitro than did anti-Ig or anti-Ig conjugated to control viral protein, comparable to the proliferation stimulated by the multivalent anti-Ig-dextran. This enhanced proliferation was dependent on binding of the conjugate to CR2, inasmuch as an anti-CD2 antibody blocked the enhanced proliferative response. This enhanced proliferative response was associated with prolonged elevations of intracellular ionized calcium, which was comparable to the response stimulated by anti-Ig-dextran. These findings suggest the use of gp350 as a carrier molecule for weakly immunogenic peptides or antigens which, when bound to gp350, would enhance B cell clonal expansion and activation of antigen-specific B cells.