Self-supported particle-track-etched polycarbonate membranes with nearly perfect cylindrical pores are used for the preparation of similarly perfect cylindrical polypyrrole nanowires and nanotubes. A complete investigation of the structural properties that result at different stages of the preparation route of polypyrrole nanowires and nanotubes is based on a combination of real and reciprocal space techniques. Nanoporous membranes with nominal pore size ranging from 5 to 150 nm and pore density up to 101 pores/cm(2) made from 21-mu m-thick polycarbonate films are used. Polypyrrole nanotubes or nanowires are synthesized inside the pores. A real-space picture of the nanomaterial results from scanning force microscopy (SFM) on ultrathin sections made in two directions to obtain structures in the sample surface as well as perpendicular to the surface. From a model-based fit to the small-angle and ultra-small-angle X-ray scattering (SAXS/ USAXS) data, the geometric pore structure is obtained and compared to values determined with scanning electron microscopy (SEM). Nanopores, nanowires, and nanotubes are described by uniform solid cylinders or hollow tubes, which are oriented highly parallel to each other and exhibit a small size distribution. Below a critical pore diameter, solid nanowires are produced whereas above this limit hollow nanotubes result.