Quorum sensing has attracted much attention due to its involvement in pathologically relevant events Such as biofilm formation, virulence factor production, and sporulation. Inhibitors of quorum sensing are important research tools and potential therapeutic agents. In this paper, we describe a phenothiazine structural scaffold as a new type of quorum sensing inhibitors with IC50 values in the single digit micro molar range in Vibrio harveyi. (C) 2009 Elsevier Inc. All rights reserved.