The vibrational spectra of triazole-thione, 1-methyl-triazole-thione, 4-methyl-triazole-thione, 1,4-dimethyl-triazole-thione and their deuterated homologues have been studied in the range 4000-200 cm - 1 . An assignment of the normal modes is proposed. From this analysis, we conclude that triazole-thione and its N-methyl derivatives exist in only one tautomeric form in the solid state. The comparison of the vibrational spectra in the solid state of 4-methyl-triazole-thione with those of solutions in various polar solvents enables us to explain the presence of two absorptions assigned to γ C H and γ N H modes of this molecule by CH and NH groups in different environments.Les spectres de vibration des triazole-thione, 1-methyl-triazole-thione, 4-methyl-triazole-thione, 1,4-dimethyl-triazole-thione et de leurs homologues deuteries ont ete examines entre 4000 et 200 cm - 1 et une attribution de l'ensemble des vibrations fondamentales a ete proposee. Il ressort de cette analyse qu'une seule forme existe pour la triazole-thione et ses derives N-monomethyles a l'etat solide. La comparaison des spectres de vibration de la 4-methyl-triazole-thione a l'etat solide avec ceux des differentes solutions dans differents solvants polaires permet d'expliquer le dedoublement des absorptions rattachees aux modes γ C H et γ N H dans le cas de cette molecule par des vibrateurs CH et NH dans des environnements differents.