Different forms of solid polyaniline (Pani) and polyaniline intercalated into montmorillonite clay layers have been characterized by solid-state deuteron quadrupole echo and magic angle spinning NMR experiments. Quadrupole echo spectra reveal different fractions of fast flipping phenyl rings for conductive emeraldine salt and nonconductive emeraldine base samples. Deuteron MAS spectra of emeraldine salt show two partially resolved sets of sidebands, whose centers are separated by 6.0 +/- 1.5 ppm. For conductive polyaniline, the temperature dependence of line widths and intensities is consistent with the existence of metallic domains embedded in a disordered insulating matrix, such that approximately 40% (T = 223 K) to 60% (T = 373 K) of the aromatic deuterons experience a Knight shift. This implies that polarons play an important role in the conductivity mechanism.