The partial molar volumes V(2)(o) and viscosity B-coefficient have been measured from density and flow time measurements for sulphanilamide, sulphanilic acid, and sulphosalicylic acid dihydrate in water and in aqueous solutions of (0.05, 0.1, 0.3, and 0.5) mol.kg(-1) sodium chloride at temperatures from (288.15 to 318.15) K, by the use of a vibrating tube digital densimeter and Micro-Ubbelohde type capillary viscometer, respectively. The transfer volumes at infinite dilution calculated from partial molar volumes have both positive and negative values. The overall positive values at higher concentrations of sodium chloride are in the following order: sulphosalicylic acid dihydrate > sulphanilic acid > sulphanilamide, which is also the order of hydrophilicity of these drugs. The interaction coefficients, partial molar expansibilities V(E)(o), and second-order derivative have also been calculated. The transfer B-coefficient values, A B, are calculated from viscosity B-coefficient data. Transition state theory has been used to calculate Delta mu(o#), the activation free energy for the viscous flow of solutions. The related activation parameters like Delta H(o#) and Delta S(o#) have been calculated. Also the excess molecular volume and contribution of various groups of the drug compound to V(2)(o) have been calculated.