A fast living radical polymerization of methyl methacrylate (MMA) proceeded with the (MMA)(2)-Cl/Ru(Ind)Cl(PPh3)(2) initiating system in the presence of n-Bu2NH as an additive [where (MMA)(2)-Cl is dimethyl 2-chloro-2,4,4-trimethyl glutarate]. The polymerization reached 94% conversion in 5 h to give polymers with controlled number-average molecular weights (M.'s) in direct proportion to the monomer conversion and narrow molecular weight distributions [MWDs; weight-average molecular weight/number-average molecular weight (M-w/M-n) less than or equal to 1.2]. A poly(methyl methacrylate) with a high molecular weight (M-n similar to 10(5)) and narrow MWD (M-w/M-n less than or equal to 1.2) was obtained with the system within 10 h. A similarly fast but slightly slower living radical polymerization was possible with n-Bu3N, whereas n-BuNH2 resulted in a very fast (93% conversion in 2.5 h) and uncontrolled polymerization. These added amines increased the catalytic activity through some interaction such as coordination to the ruthenium center.