A vibrational study of the local anesthetic procaine hydrochloride in the solid state and in aqueous solution was carried but. Assignment of the amino groups was performed using deuterated and non-deuterated samples. All the bands in the spectra were identified and assigned. The structure of the procaine cation was determined using the AM 1 semi-empirical method. A comparison with crystallographic data was made. The frequencies and intensities of the vibrations were also computed using AM1. Vibrational scale factors were employed in the AM1 calculations.