The low spectral region of procaine was studied by far-infrared spectroscopy. Raman lines were registered and interpreted. An equivalent study was performed on the molecule of benzocaine. In the characterization of the bands, and in the description of the torsion-inversion mode of thep-amino group, the AM1 semiempirical method was used. The optimum geometry parameters, the torsion and inversion potential functions, the energy levels, and the transitions were obtained. The effects of temperature on the torsion and inversion modes were studied.