Abstract: A process, carried out without a diluent or in solution, in more than 2 reaction zones, for the continuous preparation of rubber-modified polymers of vinylaromatics, wherein a monomeric aromatic vinyl compound and an elastomeric polymer, in an amount of from 3 to 16% by weight based on the monomer, are polymerized, in the absence of a free radical initiator, but in the presence of a mercaptan as a chain transfer agent, at from 80.degree. to 180.degree. C. in a first reaction zone, with stirring, up to a maximum monomer conversion, U.sub.max, given by the equationU.sub.max =K-1where K is the amount of rubber in % by weight based on monomer, and, in a second reaction zone, polymerization is continued, with stirring, to a conversion of up to about 50% by weight, after which a chain transfer agent is introduced in an amount of from 0.01 to 0.