Relations between reciprocal number average degree of polymerization and rate of polymerization derived by some workers [1] were applied to the experimental data on the polymerization of methyl acrylate initiated by benzoyl peroxide and azo-bis- isobutyronitrile at 60 °C. Chain transfer constants for benzoyl peroxide and azo-bis- isobutyronitrile are zero. Initiator efficiencies of these initiators are close to unity indi** cating that the termination reaction occurs mainly by disproportionation. The rate expressions of the initiation reaction related to the initiator concentration are given for the two initiators in question.