The densities of tetraalkylammonium perchlorates R4NClO4 (R=methyl, or ethyl, or propyl, or butyl) and ammonium perchlorate solutions in N,N-dimethylacetamide, dimethyl sulfoxide, and triethylphosphate have been measured over the whole composition range at T = 298.15 K. From these densities, apparent and limiting partial molar volumes of the electrolytes and ions have been evaluated and used to obtain the partial molar volume for the ClO4- anion. (C) 2001 Academic Press.