The temperature-concentration dependences of the activity coefficient of NaCl in aqueous solutions of 1- and iso-butanols at 288.15, 298.15, and 318.15 K. the solution ionic strength of up to 2.5m, and the alcohol contents of 0-5.66 wt% were determined by the electromotive force method using ion-selective electrodes. The results were used to estimate the interaction parameters in the Pitzer model. The reassessment of water-1-butanol and water-iso-butanol systems was carried out to improve the reliability of the recommended values of thermodynamic functions. The NRTL model was used to optimize the data on liquid-liquid and liquid-vapor equilibria in these binary systems, estimate the model parameters and errors in these parameters, and calculate the corresponding phase diagrams. The results were compared with the data published earlier. The Darken method was additionally used to calculate the excess Gibbs energy of the ternary mixtures. (C) 2011 Elsevier B.V. All rights reserved.