The low-temperature thermal properties of 3-methylpentane and 3-methylheptane were measured by adiabatic calorimetry from 10 to 330 K and 10 to 380K, respectively. Properties measured included the heat capacity of the condensed phases, enthalpy of fusion, triple point temperature, and purity of sample. The results were used to calculate the following thermodynamic functions at selected temperatures for the solid and liquid phases: - Gs(T) - H degrees (0) /T, Hs(T) - H degrees (0) /T, Hs(T) - H degrees (0), Ss, and Cs. The entropies in the ideal gas state at 298.15 K were computed, and methylene increments of 7.69 calth K-1 mol-1 for the liquid state and 9.23 calth K-1 mol-1 for the vapor state were derived. Crystallization of the 3-methylpentane sample was induced (apparently for the first time) by cooling the liquid through the liquid-to-glass transition temperature (about 77 K), followed by slow warming to temperatures between the transition and the triple point (110.25 K).