A series of initiators have been developed for living radical polymerization of methyl methacrylate (MMA) mediated by ruthenium(II) complexes [e.g., RuCl2(PPh3)(3); Ph = C6H5]. These initiators include chloromethanes, alpha-chloroesters, alpha-chloroketones, and alpha-bromoesters, among which CCl3COCH3, CHCl2COPh, and H(MMA)(2)-Br are the best to give polymers with controlled molecular weights and very narrow MWDs (M-w/M-n = 1.1-1.2). The wide variation of the initiators therefore demonstrates the generality of our transition metal-mediated living radical polymerizations. (C) 1997 Elsevier Science Ltd.