[en] Adiabatic compressibilities of several bis(tetraalkylammonium) bromide (bolaform) salts have been measured in H₂O and D₂O. Infinite dilution values of phi/sub Ks/⁰ have been obtained by extrapolation based on results determined to low concentrations. The change in compressibility at infinite dilution is not monotonic within the series although it decreases with increasing mass of the salt. Values in D₂O are more negative than those in H₂O. These observations are discussed in terms of the effect of the charged hydrophobic cations on the local solvent structure