Hydration structures of human lysozyme were analyzed by focusing on time-averaged and instantaneous hydrogen-bond (H-bond) patterns in a molecular dynamics simulation trajectory. The time-averaged H-bond patterns were significant only near the protein surface and showed good correlation with crystal-water sites found in a cryogenic crystal structure, and the H-bond networks warped the entire protein surface. The temporal persistence of the networks regarding their shape and organization depended on the surface topography. Particularly, the networks in the large active-site cleft retained their organization for a long period. The implication of H-bond networks on the biological function was discussed in referring the crystal structure of a lysozyme-substrate complex. (c) 2005 Elsevier B.V. All rights reserved.