Abstract: A high-frequency welding installation for welding particularly plastic material parts includes at least two work stations and one feed station arranged in linear succession and trays on which work pieces are conducted through the stations by means of a transport system in a single direction and are returned into the initial station in the opposite direction outside of the stations in an essentially vertically offset plane, wherein the trays are arranged during the transport in both directions always with the working side facing upwardly. Four essentially straight-line transport units are provided. The first unit is a feed unit, the third unit is a return unit, and the second and fourth units are each vertical elevators. The return unit is arranged essentially parallel to the work unit and at least the return unit operates at a higher transport speed than the feed unit.