The living anionic polymn. of isoprene [78-79-5] with n-butyllithium [109-72-8] in n-heptane in a continuous stirred tank reactor was investigated. There were no multiple steady states for monomer and initiator conversions and for mol. wts. at monomer and initiator feed concns. >4 M and >0.02 M, resp., as postulated by R.E. Porter et al. (1974), but the results might well be described by the model of H. Sinn et al. (1969).