This invention relates to a process for the preparation of non-cellular or cellular polyurethane elastomers by the reaction of(a) an organic polyisocyanate, preferably in the form of NCO groups containing prepolymers and/or modified urethane group containing organic polyisocyanates with(b) a higher molecular weight compound having at least two reactive hydrogen atoms,(c) a polyester polyol containing tin and/or titanium compounds as catalysts, and optionally(d) a chain extending agent and/or crosslinking agent in the presence of(e) blowing agents,(f) auxiliaries and/or additiveswhereby from 0.1 to 10 parts by weight, based on 100 parts by weight of the (b) component, of a polyester polyol is used as a catalyst, which is prepared by the polycondensation of organic polycarboxylic acid with multivalent alcohols in the presence of from 0.002 to 5 weight percent, based on the weight of the polycondensation mixture, of a titanium and/or tin compound used as a catalyst at temperatures from 150.degree. to 200.degree. C., as well as using this catalyst in the preparation of plastics using the polyisocyanate addition polymerization process, preferably for preparing polyurethane-plastics.