Eighteen consecutive patients with advanced and/or metastatic colorectal carcinoma have been treated with intraperitoneal administration of radiolabelled (iodine-131) monoclonal antibodies raised against different antigens associated to these kinds of tumours: anti-CEA FO23C5, anti-CEA BW494/32, anti-TAG B72.3, AUA1. The doses of isotope ranged between 21 and 150 mCi (777-5550 MBq) which delivered a radiation dose to the target tumour from 768 to 4628 cGy. Thirteen patients were previously treated with conventional regimens which consisted of chemotherapy (5-fluoracil with or without other anti-neoplastic drugs) both in adjuvant or palliative setting. Three patients are considered non-evaluable owing to concomitant chemotherapy in 2 and lack of objective parameters in 1. Out of 15 evaluable patients 2 achieved complete remission and 2 partial remission with a response rate of 26.6%. Three stable and 8 with progressive disease have also been registered. The toxicity was negligible consisting of hematologic WHO grade 1 in 7 patients, grade 2 in 1 patient and grade 3 in 1 patient, as well as hepatic WHO grade 1 in 8 and grade 2 in 2 patients. The authors conclude that this innovative way of treatment for advanced colorectal carcinoma seems to offer promising therapy; from these data, therefore, a new trial is justified employing radiolabelled MoAbs in well selected patients with metastatic or locally advanced colorectal carcinoma.