Resveratrol (3,5,4'-trihydroxystilbene) and piceatannol (3,4,3',5'-tetrahydroxy-trans-stilbene) are phytoalexins present in red grapes and wines. In vitro studies have revealed that piceatannol blocks LMP2A, a viral protein-tyrosine kinase implicated in leukemia, non-Hodgkin's lymphoma and other diseases associated with the Epstein-Barr virus, and has an antimelanoma effect on human melanoma cells. Resveratrol has several beneficial effects on human health, such as anticancer, cardioprotection, antioxidant, inhibition of platelet aggregation and anti-inflammatory activity. In this investigation, the collisional behaviour of deprotonated resveratrol and piceatannol obtained under electrospray conditions is described. The mechanisms involved in the fragmentation pattern of [M-H](-) species of the two compounds were investigated by performing MS(n) experiments, deuterium labelling and accurate mass measurements.