Favourable effects of urea and guanidine hydrochloride (Gdn HCl) on solubilization of the polar, non-polar and peptide groups of horseradish peroxidase (HRP), an example of a globular protein, provide the driving force for unfolding of HRP, in a reversible two-state process. The intrinsic or conformational stability of HRP at various pH values and temperatures has been estimated by the linear extrapolation method (LEM), a denaturant binding model (DBM) and Tanford's model. There is good agreement between these methods. Tanford's model shows that urea interacts with non-polar groups to a greater extent than Gdn HCl does, whereas Gdn HCl interacts more effectively with the peptide groups of HRP.