Thin films of plasma-polymerized pyrrole were deposited on stainless steel substrates from a parallel-plate DC reactor. They were characterized by XPS, H-1-NMR, STM, cyclic voltammetry, and by reflection-absorption infrared (RAIR) and UV-VIS spectroscopy. The films simultaneously formed on the anode and the cathode were compared. Substantial differences were found between the structures of these films, although their overall com positions were very similar. The films on the anode appeared to be less crosslinked and contained less unsaturation and conjugation than the films on the cathode. The observed effects are explained in a model in which the concurrent positive ion bombardment plays an important role in modifying the structure of a growing plasma-polymerized film.