Theory of oligomeric proteins characterises their structure as a dynamic equilibrium between the oligomeric protein and its subunits. In order to investigate this hypothesis, the kinetics of thermal inactivation of purified yeast invertase (E.C.3.1.2.26) was measured within a temperature interval of 40 - 60 degrees C. As this enzyme is supposed to be a homodimer, a model was suggested comprising a dynamic equilibrium between a dimer, D, and a monomer M, which further denaturates to an inactivated form I. The experiments were carried out at various temperatures. All data were fitted simultaneously using the Arrhenius equation for the characterisation of temperature dependence of rate constants. The differential equations describing the system (non-linear with respect to parameters as well as variables) were solved using a Runge-Kutta method. The results showed that a dimer-monomer equilibrium existed prior to starting inactivation. The activation energies of both reactions as well as the reaction enthalpy of dimer dissociation were determined. This study showed that the modelling of inactivation kinetics is a useful tool in understanding both denaturation phenomena and protein structure.