From the roots of Aconitum crassicaule three new and five known diterpenoid alkaloids have been isolated. The new alkaloids are crassicaudine [1], crassicausine [6], and crassicautine [11]. The known alkaloids are chasmanine {3}, crassicauline A {5}, foresaconitine {2}, forestine [9), and yunaconitine [10}. The isolation and determination of the structures of these alkaloids are described. The structures of the new alkaloids were established on the basis of spectral data and correlation with compounds of established structures. The structure of crassicaudine [1] was established by synthesis from chasmanine [3] The structure of forestine [9] has been confirmed by correlation with crassicauline A [5}. © 1987, American Chemical Society. All rights reserved.