Hunnemannia fumariaefolia Sweet has yielded four alkaloids, two of which, protopine and allocryptopine, are well known. A third, alkaloid F58, represented as C22H21O5N, was obtained in only minute amounts. The main alkaloid now termed hunnemanine, C20H21O5N, is phenolic, contains one methoxyl group, and on methylation yielded allo-cryptopine. O-Ethylation gave a non-phenolic base which on appropriate degradation yielded 2-methyl-3-ethoxy-4-methoxybenzoic acid, identical with a specimen synthesized for purposes of comparison. Hunnemanine is therefore 9-desmethyl-allo-cryptopine. It is the first alkaloid of the protopine type known to contain a free hydroxyl group. © 1942, American Chemical Society. All rights reserved.