Single-ion activity coefficient equations were determined for the calculation of the molality-scale dissociation constants, K-m, for n-butyric acid in aqueous NaCl or KCl solutions at 298.15 K. The activity coefficient equations are of the Huckel type, and K-m can be calculated by those for a certain ionic strength from the thermodynamic dissociation constant. The data used for the estimation of the parameters of these equations were measured by potentiometric titrations in a glass electrode cell. A new method was used to calculate the experimental K-m values from the titration data. It was based on calibration titrations of acetic acid. The activity parameters for the Huckel equation were determined from the experimental K-m values obtained by this method. The final activity parameters recommended in this study seem to be reliable. In addition to titration data, these parameters were here tested with the literature data measured on Harned and conductivity cells. K-m can be calculated for n-butyric acid in NaCl and KCl solutions by using the Huckel model almost within experimental error up to I-m of about 1 mol kg(-1)