The heat capacity of thallium(I) butanoate has been determined by adiabatic calorimetry from temperatures T of 5 K to 350 K and by differential-scanning calorimetry (d.s.c.) from 320 K to 480 K. A transition at T = (154.2 +/- 0.5) K, two very closely spaced crystalline-phase transitions at T = 285.36 K and 289.86 K as well as a crystal I-to-isotropic liquid transition at T = 456.7 K have been studied repeatedly by adiabatic calorimetry and/or d.s.c. The standard molar entropies of the several transitions are IV-to-III, 1.278[middle dot]R; III-to-II, 1.235[middle dot]R; II-to-I, 0.624[middle dot]R, and I-to-isotropic 1, 2.02[middle dot]R, respectively. Unlike higher members in this series, no mesomorphic phase occurs between crystalline phase I and the isotropic liquid phase.Supported in part by the National Science Foundation. Partial support of this research by the CICYT of the Spanish Ministerio de Educación y Ciencia (Grant in aid for scientific research PB88-127) is gratefully acknowledged.Peer reviewed