Dimethylgermathione, Me 2GeS (D 1), has been studied by vacuum pyrolysis-MS and matrix isolation IR spectroscopy. The germathione D 1 was generated in the gas phase by pyrolytic decomposition (730–900°C, 10 −2 −10 −3 Torr) of the trimer (Me 2GeS) 3 (D 3) in a quartz pyrolyzer, coupled to the ionization chamber of mass spectrometer or to an optical helium cryostat, where pyrolysis products have been frozen at 12 K in an argon matrix. The ionization energies (IE) of D 3, D 1 and its cyclodimer (D 2) have been determined from measurements of ionization efficiency curves in mass spectra of pyrolysis products of D 3 and using the semilogplot tehcnique. The IE revealed for D 1 (8.63±0.1 eV) practically coincided with that obtained earlier by PES, which proved the formation of monomeric D 1 in the reaction. In the matrix IR spectra (Ar, 12 K) of pyrolysis products of D 3 the bands 518, 574, 606, 765, 809, 850, 1231 and 1392 cm −1, disappearing simultaneously inw arming-up experimnts (to 35–40 K). These were ascribed to germathione D 1. By comparison of experimental frequencies with the calculated values the band 518 cm −1 was assigned to GeS stretching vibration. The calculated geS bond force constant (4.08 mdyn/Å) is a direct physical characteristic, giving strong evidence for considerable duoble bonding in dimethylgermathione.