The inelastic scattering of slow neutrons was used to determine the diffusive properties of water in an oriented tobacco mosaic virus solution (TMV) at 297 K. The virus concentration was 7 ± 2 % in a pH 7.0 phosphate buffer. A well developed and low angle neutron diffraction was observed with 16 à and 8 à neutrons to obtain the mean water layer thickness (310 à ) between TMV rods. In the hydrodynamic limit (at low neutron momentum transfer) no difference was found between the diffusion coefficients of the interparticle water and the buffer solution but above 1 à ^{â 1} there was a marked difference between the quasielastic scattering for these systems.