The effects of modified Collins-2 solution, adjusted lactated Ringer's solution, and a solution containing dextran 70 on kidney preservation and red blood cell (RBC) washout in dogs were evaluated. Excised kidneys were stored on ice for 24 hours and then reimplanted, at which time the contralateral kidney was removed. RBC washout from the preserved kidneys was measured at the time of initial cold flush. For 20 days after transplantation, serial measurements were made of serum creatinine, blood urea nitrogen, creatinine clearance, serum and urine osmolality, blood pH, and dog weight. No one solution cleared RBCs from the kidneys better than the other solutions. Renal function was significantly better in transplanted kidneys flushed and preserved with the Collins-2 solution than that in kidneys flushed and preserved with the other two solutions. There was generally no significant difference in function between kidneys preserved with dextran and those preserved with lactated Ringer's solution. Our findings suggest that the electrolyte composition of the flush solution may be more important than maintaining a high osmolality in the flush solution in the preservation of renal function during 24 hours' cold storage.