Experiments were performed on the quality of renal functional recovery after 24, 48, or 72-hr hypothermic storage preservation of canine kidneys in Euro-Collins solution (EC), Collins' solution C2, hypertonic citrate solutions (HC, HC-D2O), or our new flush solution 2 (F.2). Clearance tests (inulin, paraaminohippuric acid, and creatinine) and resorption rates for sodium, potassium, and glucose indicated a high superiority in the early functional recovery of F.2-preserved kidneys after all preservation periods tested. The excellent function after preservation in F.2 contrasted especially with the poor or even absent function after 72-hr preservation in HC and HC-D2O or EC. Thus F.2--a hyperosmolar solution containing sucrose with a balanced Na-K relation on the basis of "heavy water" (D2O)--is especially suitable for preservation up to 72 hr if cyclosporine is used for immunosuppression in the recipient. The recipient can be supplied with an organ with immediate good functional recovery because cyclosporine banishes the higher risk for rejection of these well-functioning organs; simultaneously, the possibility for continuous functional supervision allows avoidance of nephrotoxic side effects from the immunosuppressant.