Careful potentiostatic intermittent titrations (PITT) were performed in order to study Li+- and Mg2+ -ion insertions into the Mo6S8 chevrel phase compound. Potential dependences of equilibrium and dynamic characteristics of the insertion processes, such as the differential intercalation capacitance, C-dif, the chemical diffusion coefficient, D, and the specific ionic conductivity, K, were measured and interpreted in terms of lattice-gas models with highly attractive interactions between the inserted ions. Li-ion conductivity of the slightly intercalated chevrel phase is much higher than that of Mg-ions, which can be attributed to a higher charge density of the latter ion and to its higher polarization effect on the S-8 anions' lattice of the host material. Some crystallographic arguments related to the low mobility of the Mg-ion on the one hand, and the extremely high mobility of most of the divalent d-metal cations in the Mo6S8 chevrel phase on the other hand, are discussed. (C) 2004 Elsevier Ltd. All rights reserved.