123I-labelled iodoazomycin arabinoside (123I-IAZA) is an experimental radiopharmaceutical that has been shown to have clinical utility for imaging regional tissue hypoxia. We report the clinical pharmacokinetics of IAZA, the radiopharmacokinetics of 123I-IAZA and total radioactivity kinetics after injection of 123I-IAZA. Six healthy volunteers each received an intravenous bolus injection of 185 MBq of 123I-IAZA. Thirteen blood samples and a cumulative urine sample were collected over 28 h from each subject. A two-compartment open model best described the disposition characteristics of all three chemical components, with terminal phase half-lives of 179 +/- 24, 232 +/- 41 and 294 +/- 27 min for 123I-IAZA, IAZA and total radioactivity, respectively. 123I-IAZA had a steady-state volume of distribution (Vss) of 0.716 +/- 0.088 l.kg-1 and a systemic clearance (Cls) of 239 +/- 48 ml.min-1. Radioactive decay was responsible for about 37% of clearance; of the remaining radioactivity, about 92% was eliminated renally. Only about 12% of 123I-IAZA was eliminated unchanged in urine, indicating that renal excretion was the major route of elimination for the radioactive metabolites rather than for 123I-IAZA itself. The effective half-lives of 123I-IAZA and total radioactivity reported here are considerably shorter than previously estimated. Our results confirm that 123I-IAZA has appropriate pharmacokinetic and radiopharmacokinetic properties to support clinical hypoxia imaging.