The performance of a geologic repository for high-level nuclear waste will be influencedto a large degree by thermohydrologic phenomena created by the emplacement of heat-generating radioactive waste. The importance of these phenomena is manifest in that they can greatly affect the movement of moisture and the resulting transport of radionuclides from the repository. Thus, these phenomena must be well understood prior to a definitive assessment of a potential repository site. For this reason the Thermohydrology Research Project was initiated, An investigation has been undertaken along three separate avenues of analysis to attain the objectives of the research project: (i) laboratory experiments, (ii) mathematical models, and (iii) similitude analysis. A summary of accomplishments to date is as follows. s A comprehensive review of the literature on the theory of heat and mass transfer in partiallysaturatedporous medium was completed and documented.