Rice (Oryza sativa var. Nipponbare) possesses two different homologues of the soybean early nodulin gene GmENOD93 (GmN93). Analysis of the cDNA clones of rice homologues showed that OsENOD93a has an open reading frame (ORF) with a coding sequence homology of 58.2% to GmENOD93, whereas the ORF of OsENOD93b has displayed a homology of 42.3%. OsENOD93a and OsENOD93b genes are differentially expressed in different parts of the rice plant, as well as in cultured cells induced or non-induced with chitin oligomer. In intact rice tissues, OsENOD93b was most abundantly expressed in roots and at much lower levels in etiolated and green leaves, whereas the expression of OsENOD93a was very low in roots and etiolated leaves, and was not detected in green leaves. The level of OsENOD93a expression was enhanced markedly in suspension-cultured cells, whereas that of OsENOD93b did not increase. The application of chitin oligomer, an elicitor which induces a defence response in plants, did not significantly alter the expression of both these homologues in suspension cultures.