The solubility of two dicarboxylic acids (COOH)-(CH2)(n)-(COOH) (n=4,5; namely: adipic and pimelic acids, respectively) was determined in NaCl(aq)(0.5-4.5) mol L-1,(CH3)(4)NCl(aq) (0.25-3) mol L-1,(C2H5)(4)NI(0.25-1) mol L-1 and in pure water, at t=25 degrees C. The activity and Setschenow (k) coefficients of neutral species were calculated in all ionic media from solubility data. These coefficients, in NaCl ionic medium, were also calculated by distribution (2-methyl-1-propanol/aqueous solution) measurements. The solubility trend is (C2H5)(4)NI > (CH3)(4)NCl > NaCl. To fully characterize the acid-base behaviour of the dicarboxylic acids, the self-interaction (k(i)) parameters from solubility and distribution data and the dimerization constant (K-D) from the protonation constants in the same experimental conditions, were calculated. From these data, together with solubility ones, Pitzer and SIT parameters were calculated. (c) 2007 Elsevier B.V. All rights reserved.