The pharmacological actions of a new alkaloid, capaurine, and its O-methyl ether derivative have been studied. Capaurine was isolated from Corydalis aurea, a member of the plant family Fumariaceae, which is indigenous to Canada.The base produces paralysis in frogs and convulsions in mice and rabbits, both effects being of central origin. The heart is depressed as is the smooth muscle of the intestine and uterus. Capaurine O-methyl ether is a convulsant drug exhibiting actions on the heart and smooth muscle quite similar to those of the alkaloid itself.