We used radiolabelled monoclonal antibodies (MoAbs) to prove disease persistence after treatment for ovarian carcinoma. Twelve patients with histologically confirmed ovarian carcinoma were studied. They received 5 mCi (1 mg) of iodine-131-B72.3 by intravenous injection before and after a complete course of chemotherapy. Images were obtained with a LFOV gamma camera 2 h after MoAb administration and daily up to 6 days. Before treatment 8 patients had a true positive scan. Questionable antibody uptake was observed in 2 patients while 1 had a true negative scan and 1 a falsenegative examination. After treatment the therapeutic response was evaluated. Five patients had partial remission and antibody scan showed persistence of disease in all patients except 1. Four patients showed progression of the disease and 1 no change. The antibody scan was positive in 4 and questionable in 1. Two patients had complete remission and negative antibody scans. Computed tomography (CT) could not always discriminate postoperative fibrosis from tumour lesions, especially when the peritoneum was involved in the disease. High serum levels of tumour markers were constantly associated with the presence of tumour lesions, but normal values did not guarantee absence of disease. We conclude than the antibody scan is complementary to CT and serum tumor markers in the definition of therapeutic response.