Genomic clones containing β-tubulin sequences were isolated from a pBR322 genomic library of Tetrahymena pyriformis. Each clone has been mapped and the identity of the tubulin-related genes has been established by cross-hybridization with a cDNA containing a complete β-tubulin coding region from Chlamydomonas and by the positive hybrid-selected translation assay. The respective tubulin-related genes, βTT1 and βTT2, differ from each other although they contain a homologous region which is also homologous with a heterologous probe. Tetrahymena β-tubulin-related genes are physically linked and clustered in the genome.