Gibbs free energies of solute—solvent interactions and the Gibbs free energies of transfer for salicylic, sulphosalicylic and sulphanilic acids from water to ethanol, N-methypyrollidone, acetonitrile, N,N-dimethylformamide, dimethylsulphoxide, propylene carbonate and N-methylformamide were calculated from the measured solubility data at 25°C.K (association), ΔG (electrostatic) and ΔG (neutral) were theoretically calculated for the three acids used. It is found that the ΔG of interaction and K values of salicylic acid are larger than those of sulphosalicylic and sulphanilic acids in the organic solvents used. This behaviour is due to both inter- and intramolecular interactions of the hydroxyl and carboxylic groups of salicylic acid with the solvent dipoles.