The discrepancy in the chi interaction parameters of deuterated polycarbonate/isotactic poly(methyl methacrylate) blends as determined by the melting point depression approach and the small-angle scattering technique is reported. We have modified the Flory diluent theory by removing the inherent assumption of complete rejection of the solvent from the crystal solid by taking into consideration the crystal-amorphous, amorphous-crystal, and crystal-crystal interactions. The discrepancy in chi values obtained by the two methods is discussed.