No information exists on the organization and mechanisms of expression of the genome of rice hoja blanca virus (RHBV), a member of the tenuivirus group, but here we describe the first steps in its characterization. RHBV contains four ssRNA and three dsRNA species, the sizes of which were estimated by native and denaturing gel electrophoresis. Hybridization analyses using 32P-labelled riboprobes of viral and viral complementary polarities showed that unequal amounts of the two polarities of at least the smallest RNA are present in the virion, and indicated that the dsRNA species contain the same information as the ssRNA species of corresponding size. Total RHBV RNA directs the synthesis of two major proteins of 23K and 21K in vitro. RNA3 directs the synthesis of a 23K protein designated NS3, and RNA4 of a 21K protein designated NS4. The NS4 protein corresponds to the non-structural protein that accumulates in RHBV-infected rice tissue. The nuclecocapsid protein is not translated from either total RHBV RNA or any individual RHBV RNA in vitro.