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Biological processes often involve the surfaces of proteins, where the structural and dynamic properties of the aqueous solvent are modified. Information about the dynamics of protein hydration can be obtained by measuring the magnetic relaxation dispersion (MRD) of the water ²H and ¹⁷O nuclei or by recording the nuclear Overhauser effect (NOE) between water and protein protons. Here, we use the MRD method to study the hydration of the cyclic peptide oxytocin and the globular protein BPTI in deeply supercooled solutions. The results provide a detailed characterization of water dynamics in the hydration layer at the surface of these biomolecules. More than 95% of the water molecules in contact with the biomolecular surface are found to be no more than two-fold motionally retarded as compared to bulk water. In contrast to small nonpolar molecules, the retardation factor for BPTI showed little or no …