The present paper deals with the radical polymerization kinetics of the systems MU-AIBN-Bz-50°C and MMA-AIBN-BrBz-50°C. The rate of initiation and the k2/√k4value were determined in a broad range of monomer concentrations. The initiation rate constant was found to be independent of the concentration of solvent and monomer. In the system MMA-Bz the k2/√K4value does not change with dilution, while in the system MMA-BrBz it depends on the viscosity of the initial monomer-solvent mixture.