Lactated Ringers and Collins C2 solutions were compared in different volumes for rapid intra-aortic in situ cooling of pig cadaver kidneys. Both solutions in large volumes caused renal damage when compared with ex vivo flushed controls, although C2 was less injurious. When used for in situ cooling of human cadaver kidneys in volumes less than 1,500 ml/kidney, the two solutions were comparable and did not cause injury when compared with controls. In situ cooling permitted longer excision time (cold ischemia) and is recommended for lessening warm ischemia time in selected cases.