A method for measuring individual ionic activity coefficients is proposed and used to obtain activity coefficients of the individual ions in aqueous Solutions of NaF (about 0.02-0.99 mol kg(-1)). NaCl (about 0.01 - 1.10 mol kg(-1)) and NaBr (about 0.05-1.28 mol kg(-1)) at 298.15 K. Values of these individual ionic activity coefficients are in agreement with the literature values. The mean ionic activity coefficients of NaF, NaCl and NaBr obtained from the activity coefficients of the individual ions are ill good agreement with the literature values. In addition, dependences of the individual ionic activity coefficients upon molalities and properties of cations and anions are discussed. (c) 2008 Elsevier B.V. All rights reserved.