[en] Aim: 3-[¹²³I]iodo-alpha-methyl-L-tyrosine (IMT) is a synthetic amino acid that can be used with single-photon emission tomography (SPECT) for determinations of amino acid transport. In transformed cells, amino acid transporters may be up-regulated to support high-level protein synthesis for continuous growth and proliferation. We studied biodistribution of IMT in human colon cancer DLD-1 implanted nude-mouse KSN-slc. Materials and Methods: DLD-1 (3.0 x 10⁶ cells) were implanted into the right thigh of male nude-mouse KSN-slc (n=3 to 5) weighing 30 g, and animals were fed for 25 days to provide a 7.0 mm diameter tumor mass. Biodistribution and urinary excretion studies in mice were performed. The mice received 0.1 ml of ¹²⁵I-IMT (1.11 kBq) by injection into the tail vein. Mice were anesthetized using ether and sacrificed by heart puncture. Organ radioactivity was quantitated using a well-type scintillation counter. Results: It is presented that very high accumulation of ¹²⁵I-IMT was observed in the implanted DLD-1 tumor mass, at 60 min after intravenous injection. In biodistribution studies, tumor to other tissue ratios of ¹²⁵I-IMT accumulation in mice were 5.3 for blood, 9.8 for liver, 5.6 for intestine, 5.9 for heart, respectively. Implanted DLD-1 cells maintained up-regulated amino acid transport in nude-mouse KSN-slc. We believe this represents a good model for studying tumor imaging in vivo