The ability of a nitroxyl fatty acid (NFA) to bind specifically to albumin is abolished when, in the absence of stabilizers, a 4% solution of this protein is heated above a critical temperature of 60 degrees C. This treatment leads to the formation of "albumin polymers" as classically evidenced by GPC. Since the bound fraction is evidenced in EPR spectroscopy by a large anisotropic component, the presence of this anisotropy can be used in the assessment of the quality of the pharmaceutical preparations of albumin, which are usually pasteurized in order to inactivate viruses. Moreover, in sharp contrast with the behavior of albumin dispersions, lyophilised albumin subjected to heat treatment at 70 degrees C for 24 h left the protein untouched regarding its NFA binding and GPC profile.