Nasal absorption of insulin in rats was enhanced by addition of sodium glycyrrhetinate (GA Na), dipotassium glycyrrhizinate (GZ K₂), and carbenoxolone (glycyrrhetinic acid hydrogen succinate) disodium salt (GAHS Na₂). The latter agent was the most effective. On addition of 1% GAHS Na₂, plasma immunoreactive insulin levels in rats showed a maximum level of 0.75 mU/ml at 15 min and plasma glucose levels were decreased to about 25 mg/dl after nasal administration of 10 U/kg insulin. In a comparison of the absorption rates of insulin by nasal and intravenous (i.v.) routes in rats, nasal absorptions of 10 U/kg insulin in the presence of 1% GAHS Na₂, 0.5% GA Na and 1% GZ K₂ were 26.5%, 13.2% and 14.5% of that in the case of a 5 U/kg i.v. dose, respectively. Hemolytic activies of GAHS Na₂, GA Na and GZ K₂ were milder than those of Na caprate and Na laurate, and nasal leucine aminopeptidase activity was more strongly inhibited by GAHS Na₂ than by medium chain fatty acid salts, sodium glycocholate, GA Na or GZ K₂. Therefore, it is suggested that GAHS Na₂ is a very useful promoter which dose not irritate the nasal mucosal membrane or degrade insulin.