[en] The HER-2/neu oncogene encodes a 185 kDa phosphoglycoprotein that is overexpressed in breast, ovarian and other cancers. Seven monoclonal antibodies reactive with this oncoprotein were labeled with ¹³¹I. In vitro experiments with SKOv3 9002-18 cells determined binding affinity, internalization and degradation. The biodistribution of these antibodies in comparison to ¹²⁵I-labeled nonspecific antibody was measured in athymic mice with SKOv3 9002-18 ovarian carcinoma xenografts. Antibody 520C9 exhibited the highest and most specific retention in tumor, peaking at 17.4 ± 5.6% ID/g at 24 h