Enthalpies of solution of crown ethers (12-crown-4 (12C4) and 18-crown-6 ethers (18C6)) in the water-hexamethylphosphortriamide (HMPA) mixture and of hexamethylphosphortriamide in the mixtures of water with dimethylsulfoxide (DMSO) and N,N-dimethylformamide (DMF) have been measured within the whole mole fraction range at 298.15 K. From the results obtained, it follows that 12-crown-4 ether shows weaker and 18-crown-6 ether stronger hydrophobic properties than hexamethylphosphortriamide as shown by the curve of dissolution enthalpy 12-crown-4 and 18-crown-6 ethers in the mixture of water and dimethylsulfoxide, N,N-dimethylformamide or hexamethylphosphortriamide as well as by the preferential solvation of crown ether molecules by hexamethylphosphortriamide molecules. (C) 2003 Elsevier B.V. All rights reserved.