Twelve patients with suspected primary and recurrent carcinoma of the ovary have undergone immunoscintigraphy with an antitumour monoclonal antibody in order to assess the impact of the technique on patient management. Consistent tumour uptake of radiolabelled antibody was visualized in malignant tumours after subtraction of the blood background activity. Eight patients were imaged before surgery and in all of these the sites of uptake visualized on the images agreed with the surgical findings. In one patient with recurrent disease the imaging information was used as an aid for establishing the extent of external beam radiotherapy. A repeat study in this patient 6 months later revealed a reduction in the size of the tumour, which still concentrated labelled antibody and confirmed the viability of repeat investigations. Immunoscintigraphy was capable of providing diagnostic information which may offer an alternative to second-look surgery in these patients.