Complete nucleotide sequences of three kinds of rice beta-tubulin cDNA clones (pTUB22, R1623 and R2242) were determined. Southern hybridization indicated that these beta-tubulins consist of one gene family. Using RFLP mapping, these three beta-tubulin cDNAs were mapped to different chromosomes indicating at least three loci for the beta-tubulin gene. The deduced amino acid sequences of these cDNAs showed a high similarity to other plant beta-tubulins. The asparagine residue located at the 100th amino acid from the N-terminus of plant beta-tubulins was also conserved with these three beta-tubulins. This asparagine is thought to be responsible for the sensitivity against rhizoxin, the toxin of the pathogen of rice seedling blight, Rhizopus sp. a soil-borne microorganism. Expression of the three beta-tubulin genes was analyzed by Northern blotting and all three clones were expressed in root, the possible target tissue of rhizoxin. These results suggest that these clones are candidates of beta-tubulins targeted by rhizoxin.