We investigate the temperature effect on the size and stability of two major blood plasma proteins, human serum albumin and fibrinogen in aqueous NaCl solution. Dynamic Light Scattering measurements were carried out in the physiological temperature range up to 45°C. The analysis of the results provided the temperature dependences of the macromolecular hydrodynamic radius and the ζ-potential. For albumin the hydrodynamic radius remained unchanged, while the ζ-potential increased sharply at

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... imately 40°C. For fibrinogen the radius increased significantly above 45°C and the ζ-potential increased similar to albumin at slightly below 40°C. The dynamics of albumin macromolecule was simulated using classical Molecular Dynamics, which showed no change in the gyration radius, root mean square deviation, and the composition of disulfide and salt bridges, but substantial change in the secondary structure of the protein. We conclude that these changes in the structure and dynamics of the proteins are correlated with the qualitative change of water dynamics at 42°C in the hydration shell of the proteins.