Murine monoclonal antibody 196-14 recognizes the ovarian-cancer-associated antigen CA125, but the epitope it recognizes is different from that of monoclonal antibody OC125. We developed a human/mouse chimeric 196-14 using the variable regions of the murine 196-14 and human heavy-chain (gamma 1) and light-chain (kappa) constant regions. Cell binding and competitive inhibition assays using chimeric 196-14 labeled with 125I, 111In or 99mTc demonstrated that the in vitro immunoreactivity of the chimeric antibody was identical to that of the parental murine monoclonal antibody. However, in mice bearing human ovarian cancer xenografts, the clearance from blood was faster and absolute levels of accumulation in the tumor were lower for the 125I-labeled or 99mTc-labeled chimeric antibody than for the murine antibody labeled with the corresponding radionuclides. The tumor-to-blood radioactivity ratio was not significantly different between the chimeric antibody and the murine antibody, regardless of the radionuclide used for labeling. Chimeric antibody 196-14 labeled with 131I, 111In or 99mTc is promising for the radioimmunoimaging of ovarian cancer.