Cytomegalovirus(CMV)-specific lymphocyte proliferation in vitro was tested in the presence or absence of CMV-specific antibodies. CMV antibodies clearly enhanced CMV-specific lymphocyte proliferation but not lymphocyte proliferation induced by other antigens. Enhancement was most consistently found with cell-bound CMV antigens and often with cell-free CMV as stimulating antigen. CMV antibodies only stimulated when they were added at an early stage of the lymphocyte culture, and the stimulating effect was most pronounced at optimal and suboptimal antigen concentrations. Our data suggest that CMV antibodies stimulate CMV-specific lymphocyte proliferation at the level of antigen presentation.