1-(5-Iodo-5-deoxy-beta-D-arabinofuranosyl)-2-nitroimidazole (IAZA) has been synthesised and labeled with 125I. Radioiodinated IAZA was shown to undergo hypoxia-dependent binding in EMT-6 cells in vitro and to have an initial binding rate of 284 pmole/10(6) cells/hr at a substrate concentration of 30 microM. This binding rate is more than three times that of the reference compound, misonidazole (89 pmole/10(6) cells/hr). The elevated binding rate was accompanied by in vitro cytotoxicity 30-40 times greater than that observed for misonidazole. Whole-body elimination and biodistribution studies in BALB/c mice bearing implanted, subcutaneous EMT-6 tumors showed a rapid excretion (greater than 98% in 24 hr) with moderate tissue levels which, in general, declined as a function of blood clearance. Tumor-to-blood ratios of 4.6 (4 hr) and 8.7 (8 hr), with respective tumor uptake values of 2.08% and 1.22% ID/g of tissue, form a rational basis for evaluation of this and related 2-nitroimidazole analogs as radiopharmaceuticals suitable for scintigraphic evaluation of tissue (tumor) hypoxia.