Standard heats of solution at 25° have been determined for the isotopic pairs methanol-methanol-d, ethanol-ethanol-d, and water-heavy water in a variety of solvents. In every case, the transfer of the deuterated compound from an inert solvent (in the case of water, from the gaseous state) to a hydrogen-bonding solvent is more exothermic than the transfer of the parent compound. The isotope effect on the enthalpy of transfer shows a rough correlation with the difference between the reduced masses of the solvent-solute pair. The isotope effect on the enthalpy of the O-H bond in methanol has also been determined.