After measurement of normal renal function, dog kidneys (n = 52) were subjected to 3, 15, or 30 min of normothermic warm ischemia (WI). After 24 hr of preservation by simple hypothermic storage (SHS) in a modified Collins solution, autotransplant was done and renal function was again measured beginning at 1 hr. Compared with preharvest values, kidneys with minimal (3 min) WI had significantly decreased clearances of creatinine (Cr) and para-aminohippuric acid (PAH), PAH extraction, absolute and fractional Na reabsorption, Na excretion, and urinary Na concentration; no change in urine flow rate or K excretion; and significantly increased fractional excretion of Na, K, and H2O. Compared with minimal WI, 30-min WI produced further significant decreases in clearances of Cr, PAH, and PAH extraction; and further increases in fractional excretion of Na, K, and H2O. Urine flow was also decreased by about half and urine Na concentration rose significantly. Several parameters were very significantly correlated with the length of WI, but the most reliable index was the fractional reabsorption of Na. When several functional parameters were used together, kidneys with significant (30 min) WI prior to preservation could be identified with a high degree of statistical reliability.