The structure of rice dwarf virus (RDV) has been investigated by small-angle neutron-scattering measurements using the contrast variation method. The contrast match point gave an RNA content of about 20% by weight. The value of the neutron intensity scattered at zero angle in water divided by the virus concentration yielded a particle weight of 65.2 x 10(6). The data suggest that the viral RNA is located at radii </= 230 A and the protein between radii 230 and 360 A. These results are in good agreement with those derived from the quasielastic light scattering measurements.