Electrochemical measurements are done on (water + NaBr + K3PO4 + glycine) mixtures at T (298.15 and 308.15) K by using (Na+ glass) and (Br- solid-state) ion selective electrodes. The mean ionic activity coefficients of NaBr are determined at five NaBr molalities (0. 1, 0. 3, 0.5, 0.7, and 1) in the above mixtures. The activity coefficients of glycine are evaluated from mean ionic activity coefficients of sodium bromide. The ratio of mean ionic activity coefficient of NaBr in the (water + NaBr + K3PO4 + glycine) mixtures to the mean ionic activity coefficients of NaBr at the same molalities in the (H2O + NaBr) mixtures are correlated by using a new expression. (c) 2005 Elsevier Ltd. All rights reserved.