[en] Three monoclonal anti-CEA antibodies, designated 161, 198 (both IgG1) and 228 (IgG2a) have been labelled with ¹¹¹In via DTPA chelation and assessed for localization in human gastro-intestinal carcinomas as xenografts in athymic nude mice. Following reaction of the antibodies with DTPA anhydride, efficiency of chelation of ¹¹¹In varied between the antibodies with mean values of 30%, 52% and 62% with 161, 198 and 228 respectively. Gel filtration chromatography with all three labelled antibodies showed radiolabel predominantly coincident with IgG with little radioactivity in either high molecular weight form or as free ¹¹¹In. However, the efficiency of binding of radiolabelled antibodies to CEA producing tumour cells varied, with maxima of 42%, 65% and 20% for 161, 198 and 228. In vivo, in mice, ¹¹¹In was excreted at virtually identical rates (half times approx. 12 days) with all three prepartions and this was similar to the clearance of indium injected as ¹¹¹In-indium chloride, but ¹¹¹In-DTPA was rapidly eliminated (half time approximately 5 h). (orig.)