The thermal denaturation of lipase B from Candida rugosa was studied by intrinsic fluorescence measurement, enzyme assay and differential scanning calorimetry. The calorimetric transitions for the enzyme were irreversible and strongly dependent on the scan rate, suggesting that the denaturation is under kinetic control. It is shown that this process can be interpreted in terms of a two-state first-order kinetic mechanism, although this interpretation is not very accurate. The energy of activation for first-order denaturation kinetics calculated by different methods is ca. 260 kJ/mol.