The homo- and copolymerizations of styrene (STY) and methylmethacrylate (MMA) have been studied in the presence of several levels of benzyl alcohol (BA). From pulsed laser polymerizations it has been found that the apparent propagation rate constant increased with increasing BA for all systems. In copolymerization it has been found that the reactivity ratios for STY decrease somewhat, but those for MMA change little with increasing BA. The tacticity of poly(MMA) formed in the presence of BA is affected, the amount of mm diads increasing with increasing BA. The results are interpreted as supporting the hypothesis that BA forms a strong complex with radical chain ends terminating in MMA and a weak complex with those terminating in STY.