The subject matter of the invention is apparatuses for the aftertreatment of the exhaust gases of diesel engines. The apparatus comprises a pipe (2), through which the exhaust gases flow, a nozzle for injecting an additive into the pipe (2), and a mixing section (3) which is arranged behind the nozzle. A mixing pipe (20) is inserted into the pipe (2) adjacently to the nozzle. Said mixing pipe (20) is provided with large-area perforations (22) on the circumference, is seated in the pipe (2) with a radial spacing, has a closure cover (25) at its end with a receptacle (26) for the nozzle and, at its other end, has a funnel-shaped widened portion (23) which bears against the pipe (2) at least in regions.