Three new C20-diterpenoid alkaloids related to hetisinone were isolated from Delphinium geyeri (Ranunculaceae) and their structures determined by spectroscopic methods. The major new alkaloid, dubbed geyerine, was found to be 6-hydroxy-11-O-(2-methylbutanoyl)hetisinone. The two minor new alkaloids were 6-hydroxy-13-O-acetylhetisinone (geyeridine) and 3-acetoxy-6-hydroxy-11-O-(2-methylbutanoyl)hetisine (geyerinine). In addition to these substances, the known C19-diterpenoid alkaloids dictyocarpine, glaucenine, delcosine, browniine, 14-acetyldelcosine, 14-acetylbrowniine, 14-dehydrobrowniine, and delphatine were isolated. The total alkaloid mixture was shown to have feeding deterrent activity against the migratory grasshopper, but results on some of the purified alkaloids were equivocal. © 1986, American Chemical Society. All rights reserved.