Hydrogen atoms and water molecules around proteins and nucleic acids play a crucial role in many physiological functions. Neutron diffraction provides an experimental method of directly locating hydrogen atoms. (a) Since almost all the H atom positions can be identified experimentally, the geometrical details of certain types of H-bonds can be visualized and (b) as far as mechanistic implications are concerned, the identification of protonation and deprotonation states of certain important amino acid residues can be carried out. (c) The hydration structure around proteins and the hydration networks around DNA oligomers have been successfully characterized in several outstanding cases. These will open the new field beyond the folding structure of bio-macromolecules such as: 1) Recognition of proteins and nucleic acids through the network structure of water molecules surrounding bio-macromolecules, and 2) The nature of chemical bond in proteins and nucleic acids elucidated by the accumulation of accurate structural information of hydrogen atoms.