The information about molecular interactions in aqueous and CCl4 solutions involving 18-crown-6 (18C6) have been obtained by applying Kirkwood-Buff theory at 298.15 K. The Kirkwood-Buff (KB) integrals Gij, defined by equation Gij = integral(0)(infinity)(g(ij) - 1)4pir(2) dr, have been evaluated using the experimental osmotic coefficient (and hence activity coefficient) and partial molar volume data. The concentration range used for 18C6 is 0.001-0.035 x(2) for aqueous solutions while it is 0.01-0.14 x(2) for CCl4 solutions (x(2) being the mole fraction of 18C6). The limiting values of KB integrals, G(ij)(0), are compared with molecular interaction parameters (solute-solute i.e. osmotic second virial coefficient) obtained recently for these solutions using McMillan-Mayer theory of solutions. The agreement between two approaches is found to be satisfactory. The results of G(ij) are interpreted in terms of hydrophobic hydration in dilute concentration range and hydrophobic interaction between 18C6 molecules at higher concentrations in aqueous solutions while the same is explained in CCl4 solutions as due to weakening of the strength of solute association. The calculation of concentration fluctuation parameter N<(Deltax)(2)> indicates that considerable microheterogeneity exists in CCl4 solutions compared to that in aqueous solutions. These findings are further discussed in terms of hydrophobic hydration, hydrophobic interactions, and water structural effects as well as in terms of effects of conformational characteristics of 18C6 in presence of solvent media. (C) 2004 Elsevier Ltd. All rights reserved.