Abstract: A process is described for splitting polyurethanes and polyurethaneureas, in which the polymer is first reacted with gaseous or liquid secondary aliphatic or cycloaliphatic amines, the secondary urea formed, after removal with hydrogen chloride, is split to the isocyanate, and the polyols or polyamines also formed in the reaction are worked up and purified. It is possible by the process according to the invention to work up polyurethanes, polyurethaneureas, etc., of any origin, and to break them down into the starting materials, specifically the isocyanates, polyols or polyamines, to form starting materials in very high quality, which can be reused for the synthesis of any polyurethanes or polyureas. The invention further provides for the preparation of secondary bis-ureas from polyurethanes or polyurethaneureas or/and ureas.