The molecular structures of two new C(19) norditerpenoid alkaloids, 14-O-benzoyl-8-methoxybikhaconine [(1 alpha,6 alpha,14 alpha,16 beta)-20-ethyl-13-hydroxy-1,6,8,16-tetramethoxy-4-methoxymethylaconitan-14-yl benzoate, C(33)H(47)NO(8), (1)] and 14-O-benzoyl-8-ethoxybikhaconine [(1 alpha,6 alpha,14 alpha,16 beta)-8-ethoxy-20-ethyl-13-hydroxy-1,6,16-trimethoxy-4-methoxymethylaconitan-14-yl benzoate, C(34)H(49)NO(8), (2)], isolated for the first time from the roots of Aconitum chasmanthum Stapf ex Holmes of Pakistani origin, have been determined. The two alkaloids differ by one CH(2) moiety in a side chain (8-methoxy versus 8-ethoxy), co-crystallize in a 65 (2):35 (2) ratio, i.e. 0.65C(33)H(47)NO(8).0.35C(34)H(49)NO(8), and are inseparable by thin-layer and column chromatography. The conformations of the rings in the two alkaloids are: A and E, chairs; D, half-chair; C and F, envelopes; and B, boat. The molecular dimensions are normal; the mean bond distances are C(sp3)-N 1.463 (6), C(sp3)-C(sp3) 1.54 (2), C(sp3)-O 1.41 (2), C(sp2)-O 1.342 (3) and C=O 1.204 (4) Angstrom. There is a short intramolecular hydrogen bond with O ... O and H ... O distances of 2.556 (3) and 2.01 Angstrom, respectively.