In this article, we show that quercetin (3,3′,4′,5,7-pentahydroxyflavone), a naturally occurring flavonoid widely present in fruits and beverages (Lamson and Brignall, 2000; Day et al, 2003) and possessing anti-cancer activity (Russo, 2007; Bischoff, 2008; Murakami et al, 2008), is able to sensitise leukaemic cells isolated from CLL patients when associated with recombinant TRAIL (rTRAIL) or anti-CD95 agonistic antibody. This evidence concerns the gene FAS and cancer.