The monoclonal antibody (Mab) designated 145-9 recognizes CA125 antigen but binds to a different epitope than that recognized by OC125 antibody. This is a clinical study assessing the safety, kinetics and imaging sensitivity of Mab 145-9. Two milligrams of Mab were labeled with 111 MBq (3.0 mCi) of 131I and infused intravenously in 18 patients with ovarian carcinoma. Immunoscintigraphies were done at three, five, and seven days. There were no adverse reactions to the injection of this Mab. All immunoscintigraphies were considered positive. Immunoscintigraphy detected tumor lesions were confirmed in operative fields, in two patients with normal serum levels of CA125 and in four patients whose sonography and/or x-ray computed tomography showed negative findings. In five patients, immunoscintigraphy was repeated without any adverse reaction and revealed the progress of the carcinoma. Pharmacokinetic studies showed the steady-state volume of distribution (Vdss) to be 2772 +/- 466 ml (mean +/- s.d.), and clearance 51.3 +/- 12.7 ml/hr. In summary, immunoscintigraphies using 131I-labeled Mab 145-9 were done safely in patients with ovarian carcinoma. Preliminary results reveal a high sensitivity compared to radiological methods and tests currently in use.