Machine preservation was introduced into the Groningen Transplant Group in December 1972. Thirty five of the 90 kidneys transplanted in the following period of four years were preserved on a machine. The other kidneys were preserved by the so-called cold storage method. The advantages and disadvantages of both methods are outlined. Evidence is found in the literature and in this study that cold storage is sufficient for preservation-times up to 24 hours. When the preservation time exceeds this period, then machine preservation may be an advantage. Kidneys damaged by ischaemia were found to have a higher percentage of immediate function when preserved by the machine compared to those preserved by cold storage. There was no significant difference in one-year graft survival for the kidneys preserved by either method. Machine preservation helps to select between viable and non-viable kidneys from non-heartbeating donors. This is especially important in view of the lack of kidneys for transplantation. Therefore, in the opinion of the authors, it is necessary to continue with machine preservation in selected centres and to make the facilities of these centres available to every donor hospital in The Netherlands.