The invention relates to an apparatus for the metering of liquid media, especially varnish, of differing viscosity in an offset printing machine. Exchangeable metering subassemblies are assigned to a form cylinder. The first metering subassembly provided for processing low-viscosity media consists of a reservoir, a dipping roller, a metering roller and the form cylinder. The second metering subassembly for processing higher-viscosity media consists of a chamber doctor, a screened applicator roller and the form cylinder. In a further version, both metering subassemblies are assigned permanently to the form cylinder. Depending on the media to be processed, the necessary subassemblies are engaged with the form cylinder and the other subassembly is disengaged from the form cylinder.