Peptides encoded by truncated (S1 and S2) or full-length (S3 to S11) cDNAs of 11 of the 12 rice dwarf phytoreovirus (RDV) genome segments were expressed in a baculovirus vector system. Antibodies raised against each of the expressed peptides were used as probes to detect the authentic proteins encoded by the RDV open reading frame. Polypeptides identified as gene products of S1 to S11 in both RDV-infected rice leaf and leafhopper (Nephotettix cincticeps) homogenates were the P1 minor core (170 kDa), P2 (130 kDa), P3 major core (110 kDa), Pns9 nonstructural (83 kDa), P5 (89 kDa), Pns6 nonstructural (56 kDa), P7 minor core (58 kDa), P8 outercapsid (43 kDA), Pns9 nonstructural (49 kDa), Pns10 nonstructural (35 kDa), and Pns11a nonstructural (23 kDa) proteins. These molecular masses were in accord with those obtained from previous in vitro translation analysis. The locations of P2 and P5 remain to be determined although both of these are assumed to be outer layer proteins. Quantitative detection showed that accumulation (per gram of total proteins) of the virus-coded proteins in rice leaves is much greater (more than 15 times) than that in leafhoppers and that the content of the individual proteins varies within a sample from rice or leafhopper and also varies among different samples.