The hydrogen bonding arrangement in anhydrous beta-chitin, a homopolymer of N-acetylglucosamine, was directly determined by neutron fiber diffraction. Data were collected from a sample prepared from the bathophilous tubeworm Lamellibrachia satsuma in which all labile hydrogen atoms had been replaced by deuterium. Initial positions of deuterium atoms on hydroxyl and acetarnide groups were directly located in Fourier maps synthesized using phases calculated from the Xray structure and amplitudes measured from the neutron data. The hydrogen bond arrangement in the refined structure is in general it agreement with predictions based on the X-ray structure: O3 donates a hydrogen bond to the O5 ring oxygen atom of a neighboring residue in the same chain; N2 and O6 donate hydrogen bonds to the same carbonyl oxygen O7 of an adjacent chain. The intramolecular O3 ... O5 hydrogen bond has the most energetically, favorable geometry with a hydrogen to acceptor distance of 1.77 angstrom and a hydrogen bond angle of 171 degrees.