The invention relates to an apparatus for producing nanotubes, the apparatus being adapted to produce doped and/or undoped single-walled or multi-walled nanotubes, the apparatus comprising at least a thermal reactor. In accordance with the invention, the reactor is at least of the hottest part thereof and at least partly manufactured from a material that is at least partly sublimed into the thermal reactor as a result of the thermal reactor being heated, and the sublimed material at least partly participates in the growth of the nanotubes.