The transference number of ClOâ 4 ion in AgClO4 solution has been determined for four concentrations of salt in anhydrous DMSO at 25°C using the Hittorf method; the data were extrapolated at c= 0 by the Longsworth function. Conductivities of AgClO4 in a suitable range of concentration were also measured and the data treated with the Fuoss-Onsager 1957 equation. Based on the limiting value of the conductance of ClOâ 4 ion λ0 conductances of several ions were derived. These values differ by â 0.5 conductivity unit from the λ0 values based on the assumption that trimethyl-octadecilammonium and octadecilsulphate ions have equal mobility in this solvent.