Eleven patients with ovarian cancer have been treated with a radiolabelled monoclonal antibody directed against human milk fat globule membrane (HMFG2). All patients had Stage III disease and had previously undergone debulking surgery followed by chemotherapy. Although 16 patients have been referred, 5 could not be treated. This paper discusses the criteria for patient selection and treatment, and describes the technical difficulties of this form of therapy and the complications sustained following the intraperitoneal instillation of up to 150 mCi iodine-131 labelled HMFG2. Significant complications included two ileo-cutaneous fistulae and peritonitis in one patient which prevented treatment from being given.