[en] The radioimmunolocalisation of tumours by external scintigraphy after administration of ¹³¹I-labelled antibody to carcinoembryonic antigen (CEA) was performed in mice and patients with tumours. In mice bearing human colonic carcinoma xenografts, ¹³¹I-antiCEA was present in higher concentrations than ¹²⁵I-normal gamma globulin in normal tissues as well as tumour; however it was shown that antiCEA was retained in tumour at a maximum specificity index of 2.2 at 7 days. In the patients given ¹³¹I-antiCEA, carcinoma of the colon was readily identified; there was also a degree of non-specific uptake of ¹³¹I-antiCEA in apparently normal colon. It was also shown that ¹³¹I-antiCEA has a tendency to form immunoglobulin aggregates or immune complexes with CEA which would be cleared from the circulation by the Kuppfer cells of the liver; this should be considered if liver tumours are localised by this technique. Intensive development of the technique is continuing in order to establish its possible role in the management of patients with cancer. (U.K.)