The enthalpies of dissolution of crystalline PEO (M = 1.7 x 10(6)) and PEG (M = 3 x 10(3)) and the enthalpies of dilution of their homogeneous solutions and heterogeneous mixtures with water, toluene, and chloroform in excess of the corresponding solvents at 298 K were measured. The values of the enthalpy of mixing were calculated for the entire composition range, including the contributions from the component interaction and the destruction of crystal lattice of semicrystalline polymers. A procedure fur the separation of these contributions based on the phase diagrams of mixtures and the values of the enthalpies of polymer fusion was proposed. The obtained values of the enthalpy of interaction of PEG and PEG with the solvents agree with the published data on the enthalpy of mixing in the corresponding low-molecular-mass systems both in the sign and in the value of the change in enthalpy as well as in the pattern of its concentration dependence. The enthalpy of interaction is negative for the solutions in chloroform over the entire composition range and for the solutions in water and toluene at low and moderate polymer concentrations. The exothermal effect of interaction increases upon passing from aqueous solutions to the solutions in toluene and chloroform as well as upon a decrease in the polymer molecular mass.