The cellular and molecular mechanisms of cold storage-ATN are not well characterized. In our earlier studies, cold storage caused necrosis of human proximal tubular epithelial (RPTE) cells, whereas apoptosis was prominent during rewarming. An intriguing finding was the pronounced swelling of the mitochondria in the cold, which promoted us to further characterize its role in rewarming-associated apoptosis. Human proximal tubular epithelial cells were cold stored in University of Wisconsin (UW) solution for 48 h followed by 24 h of rewarming in regular cell culture medium. During the cold storage, there was no significant change in the Bcl-2 to Bax protein ratio, mitochondrial location of cytochrome C or caspse-3 activity. However, during rewarming, the Bcl-2 to Bax ratio increased, cytochrome C was translocated to cytosol, and caspase-3 was activated: events and timing were consistent with the occurrence of apoptosis during rewarming. In a time-course experiment, mitochondrial swelling was discernable by electron microscopy as early as at 2 h. Cold storage of isolated-mitochondria for 2 h was attended by an increase in the opening of the permeability transition pores (PTP), suggesting PTP opening as an early mechanism for mitochondrial swelling. Addition of antioxidants (deferoxamine or 2-methyaminochroman) to the storage solution suppressed mitochondrial pore opening and swelling, Bcl-2 to Bax ratio increase, cytochrome C translocation, caspase-3 activation as well as rewarming-induced apoptosis. Our data demonstrate for the first time that apoptosis following cold storage and rewarming of human renal tubular cells is accompanied by specific mitochondrial events, and that these events and apoptosis can be suppressed by adding antioxidants to the cold storage solution.