The membrane bound, tumour associated antigen CA125 is recognized by the monoclonal antibody OC125 and may be detected in tumour tissue and serum in over 80% of patients with epithelial ovarian carcinomas. A total of 13 immunoscintigrams using 111 MBq 131I-OC125 have been performed in 11 patients. The results have been compared with clinical examination, CT and ultrasound scans, surgical findings and serum CA125 concentrations. Macroscopic disease was present at the time of scanning in 11 patients (less than 2 cm, eight patients, greater than 2 cm, three patients). Clinical examination and ultrasound were positive in three, CT scanning in four, immunoscintography in seven and serum CA125 in eight patients. This pilot study suggest that serum CA125 estimation is the most sensitive indicator of disease activity. However, immunoscintigraphy using this agent may localize residual disease when clinical examination and other radiological investigations fail.