A lipophilicity scale of 14 monovalent arenediazonium ions has been established on the basis of the standard Gibbs energy of ion transfer between the 1,2-dichloroethane (DCE) and water (W), ΔG t r , i o , D C E - > W The ion transfer processes of all arenediazonium ions studied using cyclic voltammetry at the planar DCE|W interface are reversible, i.e. diffusion-controlled. Apparent values of ΔG t r , i o ' , D C E - > W estimated from the mid-point potential in cyclic voltammograms range from 17.7 to -11.3 kJ mol - 1 at 20 o C. The comparison of ΔG t r , i o ' , D C E - > W values obtained experimentally for arenediazonium ions with those for the corresponding amino substitutents obtained from a theoretical calculation of partition coefficients between W and 1-octanol evidences the importance of charge distribution over the aromatic moiety in determining the lipophilicity. The ammonium substituents of diazonium ions are 23 kJ mol - 1 more hydrophilic than the diazonium ions. The precise concentration of arenediazonium ions in W can be determined electrochemically based on the assumption that the value of the diffusion coefficient of an arenediazonium ion is the same as that of the corresponding ammonium ion.