Abstract: The use is described of monohydroxy-terminated polybutadienes as reactive or internal plasticizers for polyurethanes. The polyurethanes are made in conventional manner by reacting at least one polyisocyanate with at least one polyol under polyurethane-forming conditions, which may include the presence of a catalyst. In accordance with the invention this reaction is carried out in the presence of a monohydroxy-terminated polybutadiene which may have a molecular weight of 500 to 100,000, preferably 900 to 20,000. As a monohydroxy-terminated polybutadiene is a constituent of the resulting polyurethane, the use of a polybutadiene diol as the polyol is excluded. Short chain polyols and conventional additives may be present and the resulting polyurethane may be in the form of a solid or a foam.