urpose: Misonidazole is a radiosensitizer that binds in hypoxic cells. The purpose of this study was to find out the feasibility of I-131-Iodomisonidazole (IMISO) for imaging of tumor hypoxia. Materials and Methods: Tosyl precursor was dissolved in acetonitrile and I- 131-NaI was added to synthesize IMISO. Balb/c mice inoculated with CT-26 adenocarcinoma were injected with IMISO. Mice were sacrificed at 1,2,4,24 hr and % of injected dose per gram of tissue (%ID/g) was determined. For scintigraphy and MRI, mouse bearing CT- 26 adenocarcinoma was administered with IMISO and imaging was performed 4 hr after. Then, mouse body was fixed and microtomized slice was placed on radiographic film for autoradiography. Results: %ID/g of tumor was 1.64 (1h), 0.98 (2h), 0.85 (4h) and 0.20 (24h), respectively. At 24h, %ID/g of tumor was higher than that of all other tissues except thyroid. Tumor to muscle ratio increased with time and tumor to blood ratio also increased with time and reached 1.53 at 24 hr. On autoradiogram, tumor was well visualized as an increased activity in central hypoxic area of the tumor which corresponds to the area of high signal intensity on T2-weighted MR image. On scintigraphy, tumor uptake was visualized. Conclusion: This results suggest that IMISO may have a potential for tumor hypoxia imaging in mouse model. However, further study is needed to improve it's localization in tumor tissue and to achieve acceptable images of tumor hypoxia.