The pretransplantation viability of 28 dog kidneys was evaluated by sodium pertechnetate Tc 99m flow patterns during perfusion and preservation, in different experimentally damaged groups (warm ischemia, poor perfusate, vessel occlusion, and high temperature). The sodium pertechnetate Tc 99m test is a simple and noninvasive procedure. It clearly revealed the regional vascular distribution with segmental defects, but it was not a reliable indicator of viability in kidneys that had received warm ischemic damage prior to perfusion.