Disclosed is a method for welding together plastic parts with the aid of laser radiation having a wavelength outside the visible range. According to the inventive method, the joining zone of one of the plastic parts that are to be joined together is provided with a substantially colorless material that is transparent in the visible range of the electromagnetic spectrum while absorbing the laser radiation. The inventive method is characterized in that at least one non-ionic, laser radiation-resistant compound that has a minimum thermal resistance of 300 °C and is selected among the group comprising the polycyclic organic compounds, doped tin oxides, and hexaborides MB6 of lanthanide metals and alkaline earth metals M is used as the laser radiation-absorbent material. Also disclosed are preparations that are suitable for producing plastic parts which are welded together with the aid of laser radiation whose wavelength lies outside the visible range, said preparations containing: a) a thermoplastic matrix polymer that is suitable for embodying the plastic parts; b) at least one essentially colorless, non-ionic, laser radiation-resistant material which is transparent in the visible range of the electromagnetic spectrum, absorbs the applied laser radiation, has a minimum thermal resistance of 300 °C, and is selected among the group comprising the polycyclic organic compounds, doped tin oxides, and hexaborides MB6 of lanthanide metals and alkaline earth metals M; c) one or several optional UV stabilizers; and d) other optional additives.