This experiment was aimed to investigate the changes in the blood flow (splenic arterial blood flow; S.B.F and pancreatic tissue blood flow; P.T.B.F) and the changes of production of prostaglandins (prostacyclin and thromboxane A_2) in canine segmental pancreatic graft before and after transplantation. Furthermore, we investigated correlation between the blood flow of the transplanted pancreas (S.B.F and P.T.B.F) and the changes of production of these two prostaglandins in it according to preservation time after transplantation. This experiment consisted of 17 dogs divided into two groups; short-term (3 hours) preserved group (group I, N=12), long-term (24 hours) preserved group (group II, N=5). In group I, after transplantation, both S.B.F and P.T.B.F increased significantly with enhanced production of prostacyclin. While, in group II, they decresed significantly with enhanced production of thromboxane A_2 and reduced production of prostacyclin. Graft function was monitered by daily fasting blood glucose level in each 5 dogs of both group. Four dogs in group I and only one dog in group II survived with functioning grafts for two weeks. But in group I, one graft was lost at 4 days from vascular thrombosis. On the other hand, in group II, two grafts were subsequently lost at 1 and 8 days from vascular thrombosis and the other two grafts were never functioning after transplantation. These results suggested that there was a significant correlation between the productive system of prostacyclin & thromboxane A_2 and the blood flow of the transplanted pancreas in canine segmental pancreatic transplantation, and enhanced production of thromboxane A_2 might be responsible for vascular thrombosis after transplatation. For this reason, good function of the graft after segmental pancreatic transplantation may be possible by inhibiting the production of thromboxane A_2,even if preservation time is long.