The purpose of this paper was to investigate in vivo behavior of biodistributionand elimination of myocardial viability imaging agent 125I-IPPA. Myocardial uptakeof 125I-IPPA in rats showed a peak of 4.4% of injected dose per gram at 1 min. Thehalf elimination time of myocardium was 3.8 min. The maximal uptake of thyroid wasonly 0.005%ID/organ at 120 min. The initial half time of 2.7 min in rabbits wasobtained from the elimination curve of radioactivity in blood. In vitro binding test for125I-IPPA to HSA showed rather constant level of activation during the two hours.The second peak of extraction was observed in major organs of rat