Two human monoclonal antibodies, HID-7E7 and ROB-6F2, were produced by EBV transformation of peripheral blood lymphocytes (PBL). PBL were obtained from a patient with ovarian cancer who had been exposed several times to a Tc-99m labeled murine monoclonal anti-CA 125 antibody (B43.13, Biomira, Edmonton) for immunoscintigraphy. The HID-7E7 and ROB-6F2 producing B-cells were cloned with a limiting dilution technique and have shown stable immunoglobulin secretion within a period of three years. The human monoclonal antibodies HID-7E7 and ROB-6F2 are of the IgG isotype, and bind with significant affinity to the murine monoclonal antibody B43.13, which was used for immunoscintigraphy. Binding affinity of ROB-6F2 to other murine antibodies could not be detected. Cross reactivity of HID-7E7 to a murine anti-CEA monoclonal antibody was observed. In order to verify the anti-idiotypic character of the generated human antibodies, the ability of HID-7E7 and ROB-6F2, respectively, to inhibit the formation of the CA125/B43.13 complex is demonstrated via an enzyme-linked immunosorbent assay. These human anti-idiotypic antibodies are possible candidates for immunotherapy of ovarian cancer in patients with a small tumor burden following surgery and/or chemotherapy.