Recently, a major resection of the pancreas has been carried out not only to treat carcinoma of pancreas but also chronic pancreatitis. But limited and often contradictory reports have been made on the exocrine effects after partial surgical pancreatectomy in mammals. It was suggested that the growth of the residual tissue in pancreatectomized rat is very active, because pancreas has the great power of regeneration after partial pancreatectomy, while others observed that rat pancreas after partial surgical resection revealed a perplexing mixture of atrophy and regeneration of acinar tissue. On the other hand, another results showed that the amount of insulin required to control diabetes after partial resection of pancreas is much greater than that needed after total pancreatectomy. Because the anti-insulin system, such as glucagon secretion and hypophyseoadrenal function, is probably depressed after total pancreatectomy. Furthermore, minimal resection line which will not influence the normal function of pancreas is not agreeable, such 75%, 80% or 95% resection of the total pancreas in rat. So far, studies on the exocrine function other than endocrine function after partial pancreatectomy have been limited. Therefore, the main purpose of this study is to examine the changes of exocrine as well as endocrine function of pancreas at the different time interval after 60% or 80% pancreatectomy in rats. The results summerized as follow: 1) In both 60% and 80% resected groups, a slight decrease of the total body weight was observed at a day after partial pancreatectomy in rats, but the body weight was continued to increase for following 100 days. 2) The weight of residual pancreas was continuously increased during experiment in both 60% and 80% resected groups. But the content of tissue protein in residual pancreas was significantly decreased comparing with those of resected pancreas. 3) The flow rate of pancreatico-biliary juice was significantly decreased immediately after pancreatectomy in both resected groups. But it was recovered to control level after a day in 60% resected group, after 30 days in 80% resected group. 4) The output of amylase and lipase in resected groups were significantly decreased right after pancreatectomy comparing with control group. In the 60% resected group, the output of amylase was recovered during the following 100 days after pancreatectomy, while lipase output in 3 days. However, in the 80% resected group, the output of amylase and lipase were not recovered during 100 days after pancreatectomy. 5) In order to examine the endocrine function, blood sugar level were examined at all experimental periods after partial pancreatectomy. There was no difference between control and 60% resected group in the sugar level. But in the 80% resected group the level was significantly incresed immediately after pancreatectomy, and reached the highest level at 3 days. Then it was decreased to control level during the next 10 days after pancreatectomy. The above results showed that in 60% resected group little changes were observed on pancreatic function, but severe functional impairments were observed in 80% resected group. This results suggested that the endocrine function was recovered within a short period, although the exocrine function was not recovered for a long time after 80% pancreatectomy in rats.