The unfolding and further denaturation of IgG and its Fab and Fc fragments were studied both on a macroscopic and molecular level, using differential scanning calorimetry and circular dichroism spectroscopy, respectively. It was shown that the structural integrity of the Fab and Fc units was retained after fragmentation of the IgG. The Fab fragment denatured at ∼61°C and the Fc fragment at 71°C. The structural transitions observed in the whole IgG is the sum effect of those determined for the isolated Fab and Fc fragments.