A method for detn. of the propagation rate coeff. (kp) for radical polymn. of 1,3-butadiene in ClC5H6 as solvent and with 1,1'-azodicyclohexanecarbonitrile as initiator was described. The data were interpreted in terms of Arrhenius plots for kp and av. no. of radicals per particle and ratio of coeffs. for radical exit and radical entry from or into latex particles vs. particle diam.