Khat, the young leaves of Catha edulis Forsk. (Celastraceae), is widely used in East Africa and the Arabian peninsula as an amphetamine-like stimulant due to its content of cathinone, norpseudoephedrine, and norephedrine. Merucathine, the pentenyl-analogue of norephedrine, has recently been found, and further chemical and spectroscopic studies have shown the (3R,4E)-configuration instead of the originally postulated (3S,4E)-configuration. Merucathinone and pseudomerucathine, the analogues of cathinone and norpseudoephedrine, have only been identified by gc/ms and hplc with photodiode array detection until now. In this report, we describe the isolation and structure elucidation of the phenylpentenylamines merucathinone, pseudomerucathine, and merucathine as their acetyl derivatives. Considering the low concentration in khat and the known instability of keto-khatamines, particularly as free bases, the phenylpentenylamines were extracted as oxalates and separated as acetyl derivatives. Recent in vitro studies showed their pharmacological activity, but they play only a minor role concerning the psychoactive effects of khat. Many phenanthrene stilbenoids have been isolated from plants of the Orchidaceae and are considered to play important roles as phytoalexins. Our present work describes the occurrence and structural elucidation of a new stilbenoid from Dendrobium chrysanthum Wall. ex Lindl. The new compound was isolated from an EtOH extract after Si gel chromatography and exhibited C18H20O5 (M+ 304). Its 1H nmr spectrum indicated two singlets (2.80 ppm for two pairs of methylene protons of a bibenzyl system and 6.36 ppm for protons at C-2 and C-6) and an ABX system (assignable to protons at carbons-2', 5', and 6'), in addition to three methoxy and two hydroxy groups. The ms showed two conspicuous fragments at m/z 167 (a benzyl fragment bearing a hydroxy and two methoxy groups) and 137 (a benzyl fragment bearing one hydroxy and one methoxy group). By comparison with a synthetic stilbenoid and nOe experiments, the structure was concluded to be 4,4'-dihydroxy-3,3',5-trimethoxybibenzyl.