Glucagon was administered exogenously via a subcutaneous route to totally depancreatized adult mongrel dogs and studies were made with major emphasis on glucagon effect on the plasma glucose levels. 1. In the totally depancreatized dogs, the plasma glucose levels determined 90 minutes after glucagon injection (40 micrograms/kg s.c.). were compared with the pretreatment fasting plasma glucose levels. The rate of increase in the plasma glucose levels was 5.13 +/- 0.48 times (M +/- SEM) in dogs with low pretreatment level (lower than 100 mg/dl). In dogs with higher pretreatment levels (100-400 mg/dl), the increase was 1.62 +/- 0.40 times. And in dogs with the pretreatment levels higher than 400 mg/dl, the value was 0.90 +/- .07 times. 2. Ninety minutes after regular insulin injection (0.25 U/kg i.v.), glucagon was administered (40 micrograms/kg s.c.), and the changes in the plasma glucose levels were determined. 3. In totally depancreatized dogs, a transient increase in the plasma insulin level was noted when glucagon was administered (40 micrograms/kg s.c.) under infusion of a mixture of glucose and insulin. 4. There was no significant difference in the rate of disappearance of glucagon from the blood between normal and totally depancreatized dogs. 5. It is considered that glucagon would be useful for the treatment of hypoglycemia encountered after total pancreatectomy.