The following values of monomer reactivity ratios were found: r(S) = 3,3 +/- 0,3; r(B) = 0,12 +/- 0,02 (cyclohexane, 25 degrees C). The comparison of the kinetic parameters obtained with Li, Na and K counter-ions shows that the great difference between coordination polymerization with Li and ''typically anionic'' polymerization with K is mainly determined by the variation of the cross-propagation rate constant k(BS) with the nature of the counter-ion. No evidences for the specific role of the solvation of Li counter-ion with butadiene monomer were found.