The proportion of tubulin and its isoform pattern have been analyzed at different stages in the development of Drosophila melanogaster. Tubulin proportion varied during development, the highest proportion being found at embryogenesis where two alpha- and beta- (one of them transitory) tubulin subunits were found. During the larval stage, the proportion of total tubulin decreased but new alpha-isotubulins were identified. These alpha-isotubulins were also present at the adult stage and all of them could be incorporated into microtubules assembled in vitro.