SUMMARY Kidneys have been preserved for 24 hr by two methods—continuous hypothermic perfusion with plasma protein fraction (PPF) and simple ice storage method of Collins et (3). Prior to preservation, the kidneys were subjected to warm ischaemic intervals varying from 0 to 180 min. Kidneys preserved without warm ischaemia functioned immediately whichever method was used. Kidneys preserved by perfusion after up to 60 min warm ischaemia returned to normal function. Kidneys preserved by Collins' method did not function if the warm ischaemic interval exceeded 30 min. As the warm ischaemic interval was increased, there was a proportional rise in renal vascular resistance.