Abstract: A solvent-containing composition for the cleaning of equipment used to mix and handle reactive multicomponent mixtures of high viscosity, which react to form polymers. In order to improve the capacity of the solvent to dissolve the more or less polymerized mixtures, the solvent contains a chain-terminating agent. For binary systems containing liquid polysulfide polymers, the solvent contains a chain-terminating agent or chain-degrading agent containing mercapto group-containing compounds of the general formula R--SH or disulfide or polysulfide group-containing compounds of the general formula R--S.sub.n --R, in which formulas n.gtoreq.2 and R represents equal or difficult alkyl residues, aryl residues or substituted alkyl or aryl residues. For binary polyurethane systems, the solvent contains chain-terminating compounds which in their molecule contain a Zerewitinoff-active hydrogen atom and have the general formula HY--R.sup.1, wherein ##STR1## where R.sup.2 =H or alkyl and R.sup.