A method for producing an active substance-containing polyurethane plaster for transdermal application is described, said plaster containing at least one active substance at a highly accurate declared dose. In the described method, a solvent-free active substance-containing polyurethane is produced by reactively coating a solvent-free active substance-containing polyurethane material (40), which is mixed in a coating unit (60) immediately before or during the application process, onto an elastic backing foil (20) that has been rendered non-extensible at least in the direction in which the applied polyurethane material is processed by means of a supporting, adhering auxiliary foil (30) which is at least mono-axially non-extensible.