. Setschenow coefficients have been derived from solubility measurements on cyclohexane, benzene, naphthalene, 1-naphthol, 1,5-dihydroxynaphthalene, and anthracene in alkali halide, tetraalkylammonium bromide, and tetraphenylarsonium chloride aqueous solutions at 298.2 K. Single ion Setschenow coefficients have thence been obtained by an assumption involving extrapolation of the tetraalkylammonium bromide results to zero cation volume. Setschenow coefficients for the tetraalkylammonium cations correlate well with a hydrophobicity parameter based on their transfer chemical potentials from water into 1,2-dichloroethane.