Octamethylcyclotetrasiloxane is presented and investigated as probe liquid for NMR cryoporometry or DSC-based thermoporometry. This compound which may imbibe into both hydrophilic and hydrophobic pores is shown to exhibit a melting point depression that is larger than that for other cryoporometric probe materials such as cyclohexane. The transverse relaxation time differs by more than three orders of magnitude between the solid and liquid states, separated by a sharp phase transition. Hence, as demonstrated in controlled pore glasses, octantethylcyclotetrasiloxane can provide pore size distributions for materials with pore sizes up to the micrometer range. (c) 2006 Elsevier Inc. All rights reserved.