With the aid of data pooled from 51 transplant centers, a total of 83 human kidneys stored by simple hypothermia with and without initial perfusion were evaluated. Of the 81 shared kidneys for which data could be collected, only 4 cases of nonfunctioning kidneys were reported. Collins' solution and Ringer's lactate solution were found to yield superior results to surface cooling at periods under 15 hr of cold ischemia. Of kidneys stored in Collins' C-4 solution for 7-14 hr during transcontinental transport, 10 of 12 functioned immediately and 2 functioned after an initial brief period of oliguria. Immediate function was obtained in spite of warm ischemia times of 15-25 min using C-4 solution in 6 out of 7 transplants.