Two monoclonal antibodies to carcinoembryonic antigen (CEA) were radiolabelled with 131I and used for the treatment of hepatic metastases in a patient who had a primary colonic carcinoma. Approximately 100 mCi of 131I-labelled antibody were administered via the hepatic artery on two occasions. On the second occasion, radiolabelled antibody was given concurrently with biodegradable starch microspheres in an attempt to enhance tumour uptake of antibody by achieving temporary stasis or delay of hepatic blood flow. The procedure was carried out uneventfully. There was clinical improvement and a fall in circulating CEA levels after each course of treatment. Furthermore, after the second course of therapy the clinical improvement was sustained for a longer period (more than 3 months) and there was evidence of diminution in the size of some of the liver metastases. Regional administration of 131I-labelled anti-CEA antibody concurrently with biodegradable starch microspheres appears to be a promising new method for the treatment of hepatic metastases from colonic carcinoma.