Rat kidneys were flushed with isotonic citrate solution, hypertonic citrate solution or Collins''s C2 solution and were stored hypothermically for 24 h before transplantation into another rat of the same inbred clony. The number of animals surviving for 1 mo. was greatest with isotonic-citrate-flushed kidneys (82%), and lest with Collins''s C2 solution (27%). Functional and morphological damage after transplantation was consistently greater in Collins''s-flushed grafts, as compared with citrate-flushed grafts. Best results were attained with the isotonic-citrate flushed grafts. Seven days after contralateral nephrectomy all surviving animals had elevated serum creatinine and urea concentrations, along with decreased creatinine clearance, and they had secreted large volumes of dilute urine. Renal function was best in animals with isotonic-citrate-flushed grafts. After 1 mo., significant improvement in urine osmolality, creatinine clearance and serum creatinine had occurred only in the rats with citrate-flushed grafts. There were no significant differences between the citrate groups. All surviving rats had some residual renal cortical damage, but severe interstitial nephritis (> 30%) was much less frequent in the citrate groups.