Two-dimensional gel electrophoresis (2D-PAGE) patterns of seed embryos were compared between a long culm cultivar, Norin 29 and its semidwarf near-isogenic line, SC-TN1, in rice (Oryza sativa L.), and thereby two proteins apparently related to semidwarfism were identified. The proteins found in Norin 29 and SC-TN1 were designated as semidwarfism-related protein (SRP)-1 and SRP-2, respectively. The crossing tests showed that SRP-1 and SRP-2 were controlled by codominant alleles at a single locus, and that this locus was linked with the semidwarfing gene sd-1 locus. The partial amino acid sequences determined were highly homologous with those of storage protein glutelin α subunits in the seed endosperms. In the seed endosperms of Norin 29 and SC-TN1, a total of 8 glutelin α subunits were identified by 2D-PAGE. The amino acid sequences of SRP-1 and SRP-2 were identical with the glutelin α5a-and α5b-subunits, respectively, which existed in both endosperms and embryos unlike the other glutelin α subunits.