The enthalpies of dilution of d-sorbitol and d-mannitol with water and aqueous sodium halide solutions were determined by isothermal microcalorimetry at 313.15 K. Experimental enthalpies of dilution varying with the concentration of the polylols were correlated with the virial expansion equation that was obtained with the McMillan−Mayer theory. Enthalpic interaction coefficients h 2, h 3, and h 4 in the equations have been determined, and the values of the pairwise enthalpic interaction coefficient (h 2) are discussed in terms of solute−solute and solute−solvent interactions.