Intranasal glucagon can raise blood glucose levels in healthy subjects. The aims of this study were to 1) compare the hyperglycemic effect of intranasal and intramuscular glucagon in healthy subjects and type I (insulin-dependent) diabetes patients during euglycemic conditions and 2) test the efficacy of intranasal and intramuscular glucagon in counteracting hypoglycemic episodes in insulin-treated diabetic patients. Intranasal glucagon raised blood glucose levels in both healthy subjects and type I diabetic patients, the effect of intramuscular glucagon being similar for the first 30 min and higher thereafter. Intranasal glucagon was also quicker acting than oral glucose in healthy subjects. Intranasal glucagon raised blood glucose levels in patients with hypoglycemic episodes, although less effectively than intramuscular glucagon. These data indicate intranasal glucagon as a possible emergency remedy for self-medication in insulin-treated patients prone to hypoglycemic episodes.