Isotope effects on the heats of solution of the isotopic pairs chloroform/chloroform-d and acetone/ acetone-d6 have been measured in a variety of solvents at 25°. While both positive and negative isotope effects have been observed for the heats of solution of these solutes, the transfer of the deuterated compound from cyclohexane (at infinite dilution) to other solvents is in every case more exothermic than the transfer of the parent compound.