Electrochemical and mass transport properties of a thiolate/disulfide couple, formed by 5-mercapto-1-methyltetrazole lithium salt (LiT) and disulfide (T-2) dissolved in liquid poly(ethylene glycol) 500 dimethyl ether, PEG(500), DME and soft methoxy-linked poly(ethylene oxide), PMEO, have been studied using a three-electrode microcell and a conventional three-electrode cell. Cyclic voltammetry showed that the electrochemical reversibility of the redox couple is poor in both solvents. The exchange current densities for the reduction and the oxidation reactions in PEG(500) DME-LiClO4 are 0.24 mu A cm(-2) and 0.13 mu A cm(-2), respectively. The diffusion coefficients of T- and T-2 in the same system are 7.88 x 10(-8) cm(2) s(-1) and 6.01 x 10(-8) cm(2) s(-1), respectively, at 23 degrees C, which are about 40 times higher than those measured in PMEO-LiClO4. The diffusion coefficients or T- and T-2 in polymer electrolytes based on PMEO showed a VTF behaviour. The diffusion coefficient of T- increases (i) with decreasing LiT concentration and (ii) when T-2 species are present in the electrolyte.