Human monoclonal antibodies (HMAbs) to human cytomegalovirus (HCMV) have been developed by using electric field-induced cell fusion of human B lymphocytes to the human-mouse cell line SBC-H20. By this procedure, multiple hybridomas have been produced that secrete IgG 1 HMAbs with distinct patterns of indirect immunofluorescence on HCMV-infected cells. HMAbs Z01 and X20 immunoprecipitated a major protein at 64 kDa. HMAb Z02 immunoprecipitated a major protein of 48-50 kDa. HMAb Z10 identified a single protein at 65 kDa and HMAb X16 identified proteins at 100, 65, and 36-38 kDa. The HMAbs demonstrated varying degrees of virus-neutralizing activity. The production of HMAbs to HCMV provides an important approach to studying the human host response to HCMV by elucidating biologically relevant antigens and epitopes. In addition, HMAbs are a potentially unlimited source of relevant human antibodies for treating life-threatening HCMV infection.