The thermostability of pure yeast alcohol dehydrogenase was investigated at various temperatures, in the presence and absence of sucrose, by both activity assay and differential scanning calorimetry. The thermal inactivation exhibited nonlinear biphasic behavior. The thermal inactivation rate constants and the magnitude of the heat-stable and heat-labile fractions of the enzyme were quantified. The values of the denaturation temperature were experimentally measured by calorimetry. It was found that although activity assay and calorimetry are based on different principles, they yield results that agree well with each other. However, each technique provides unique data (e.g. enzyme activity vis-a-vis basic thermodynamic properties, such as the denaturation enthalpy) and the two techniques may be considered complementary to each other.