Evidence is provided that, with cold ischemia up to 48 hr and warm ischemia up to 60 min, simple storage preservation results in equally good or better transplant success rates than pulsatile machine perfusion. In the critical 24- to 43-hr preservation period, 1-year survival rates were 53 +/- 3% for 282 kidneys preserved in Collins solution, as compared with 40 +/- 2% for 565 kidneys on the Belzer machine (P less than 0.0001) and 48 +/- 1% for 1441 kidneys perfused on the Waters machine (P = not significant). Warm ischemia of 40 to 60 min also yielded better results with simple cold storage than with machine preservation (P less than 0.05). Although it has been maintained that one of the functions of preservation machines is to select out kidneys of poor quality, we found that this preselection actually has resulted in lower transplant survival rates. Because storage in Collins solution is simpler, safer, and much less expensive, we conclude that there is no longer any reason to preserve kidneys by pulsatile perfusion on machines.