The kinetic parameters of the thermal decomposition of tetrazole and 5-alkyl- and 5-aryl-substituted tetrazoles in melts of neat substances and in nitrobenzene solutions have been determined using the manometric method. The limiting stages of the monomolecular decomposition, which determine the observed rate of nitrogen formation, include the fast reversible transformation of the lH- and 2H-forms and the reversible opening of the 2H-form followed by the formation and subsequent cleavage of the corresponding intermediate diazo compound.