The two-layer cold storage method (TLM) using University of Wisconsin (UW) solution supplies sufficient oxygen to pancreatic grafts during preservation and extends pancreas preservation time to up to 96 h in the canine model. Simple cold storage in UW (UWM) on the other hand, preserves canine pancreas grafts for up to 72 h by preventing cell swelling, mainly because of its high osmotic pressure. The aim of this study is to analyze morphologically dog pancreatic grafts preserved by these two methods with their different mechanisms. Immediately after preservation of canine pancreata by TLM for 72 h and 96 h (group 1 and group 3, respectively), and by UWM for 72 h and 96 h (group 2 and group 4, respectively), tissue ATP levels were determined using high-performance liquid chromatography (HPLC), and detailed morphological analyses of intragraft components were performed using light- and electron microscopy. The mean areas of one mitochondrion and rough endoplasmic reticulum (RER) vacuolization were calculated by computer-graphic analyses using NIH image 1.62 f soft. The tissue ATP levels were significantly higher in groups 1 and 3 than groups 2 and 4 ( P < 0.05). Light microscopy demonstrated no marked difference among the 4 groups. By electron microscopy however, mitochondrial swelling and RER vacuolization were observed in acinar cells to various extents in the 4 groups. They were significantly more evident in group 2 than group 1 ( P < 0.05), and in group 4 than group 3 ( P < 0.05). In conclusion, TLM demonstrated excellent protection of intracellular organelles, mitochondria, and RER, up to 72-96 h. Well-maintained graft ATP levels in TLM groups may result in maintaining the integrity of intracellular organelle membranes as well as cellular membranes.