Sorghum SbSTS1 was the first example of a stilbene synthase gene in monocots. Previously, we demonstrated that the gene was involved in defense responses. To examine its biochemical function in planta, SbSTS1 was overexpressed in transgenic Arabidopsis. Metabolite analysis revealed that cis-resveratrol glucoside (piceid) accumulated as the major stilbene in the transgenic lines. Using liquid chromatography-tandem mass spectrometry (LC-MS/MS) in selected reaction monitoring mode, up to 580 microg g(-1) FW of cis-piceid were detected in 2-week-old plants, which represent a convenient source of the cis-isomers for pharmacological investigations. Our results also suggested the presence of unknown stilbene isomerase activities in Arabidopsis.