A series of oxorhenium(Ti) SNS/S mixed-ligand complexes [ReO(L-n/L)] carrying different types of tridentate ligands (L-n) and the same monodentate coligand (L) [L = C6H5S, L-1 = C2H5N(CH2CH2S)(2) (1), L-2 = (C2H5)(2)-NCH2CH2N(CH2CH2S)(2) (2), L-3 = C2H5SCH2CH2N(CH2CH2S)(2) (3), and L-4 = 2,6-(SCH2)(2)NC5H3 (4)] have been synthesized and characterized by spectroscopic methods and elemental analyses. X-ray structure determination was performed for complexes 3 and 4. Complex 3 adopts the expected distorted trigonal bipyramidal geometry around the metal in a syn configuration, while complex 4, due to the aromatic character of the nitrogen of the SNS donor-atom set, exhibits a distorted square pyramidal geometry. The interaction of complexes 1-4 with glutathione (GSH) was studied by high-performance liquid chromatography, revealing the rapid formation of the respective daughter complexes 5-8, wherein the L coligand has been substituted by GS. The daughter complexes 5-8 have been characterized by ES-MS and 2D NMR spectroscopy. Kinetic aspects of the interaction of complexes 1-3 with GSH have been studied by isothermal titration microcalorimetry providing direct measurements of the interaction rate constants as well as of the total enthalpy change. The reaction of complex 1 exhibits the slowest rate and that of complex 2 the fastest. This is in agreement with previously reported tt ends for analogous Tc-99m complexes.