Abstract The tetrazole–azide tautomerization of some halogen-substituted tetrazolo [1, 5-a] pyridines was examined by IR spectroscopy at ambient temperature and by 1 H, 13 C and 15 N NMR spectroscopy at various temperatures. The tetrazolopyridines can exhibit equilibrium between the azide and the tetrazole forms. For some of them slow exchange occurs on the NMR time-scale, such that it is possible to estimate equilibrium constants. ...