Two new derivatives of monoterpene alkaloids, named incarvillateine C and incarvillateine D which are related to an antinociceptive alkaloid, incarvillateine, were isolated from the aerial parts of Incarvillea sinensis LAM. On the basis of both chemical and spectroscopic evidence, the structures of the first two were characterized as a bis-demethoxy and demethoxy derivatives of incarvillateine, respectively. (C) 1999 Elsevier Science Ltd. All rights reserved.