Bud exudates of Populus simonii and Populus yunnanensis were similar and contained primarily caffeic acid and its esters together with the flavanones pinocembrin and pinobanksin-3-acetate. The terpenoid patterns of the specimens examined varied, but this variation was not species related. On the basis of bud exudate analysis P. simonii and P. yunnanensis may be considered to represent a single species.