1,2,5-Thiadiazoles 1-5 bearing CN, CONH2, SCH3, and Cl substituents have been investigated under electron impact conditions. Collisional activation (CA) and neutralizatiun-reionization (NX) mass spectrometries have allowed the identification of new nitrile N-sulfides (NCCNS, H2NCNS, H3CSCNS, and ClCNS) as ions or neutrals in the gas phase of a mass spectrometer, These results were supported by chemical ionization experiments of nitriles using carbon disulfide as the reagent gas, flash vacuum pyrolysis experiments, and ab initio molecular orbital calculations at the G2(MP2,SVP) level. The neutral nitrile N-sulfides are found by experiment and theory to be observable species in the gas phase. All the cations are potential energy minima, and their calculated fragmentation energies are in accord with experimental observations.