Three α-tubulin isoforms were previously detected in Neurospora crassa. We have cloned and analysed two α-tubulin cDNAs, Tub αA and Tub αB that encode polypeptides of 453 and 451 amino acids, respectively. The encoded amino acids exhibit an unusual divergence of 35%. This is the highest divergence ever observed between α-tubulins from the same species. The expression of the two genes is developmentally regulated. We did not detect any transcription of the Tub αA gene in dormant macroconidia and during the first 30 min of development even though the α-tub A protein is already present in the early stage of germination. In contrast, the Tub αB gene is continuously transcribed during the vegetative cycle and the expression profile of the protein follows the ones of its mRNA.