The anisotropic proton conductivity of a large-sized single crystal of the supramolecular, commensurate host-guest inclusion compound constituted by a polyanionic thiourea-chloride matrix defining channels in which the diquinuclidinium cations [Q(2)H](+) are hosted is reported. Specimens in the millimetre scale display an anisotropy factor of about 100, with electrical conductivities along molecular channels of the order of 10(-4) S cm(-1) at room temperature.