The presence of glutamylated tubulin, a widespread posttranslational modification of α- and ß-tubulin, has been investigated in Drosophila melanogaster using the specific monoclonal antibody GT335. We show here that this modification is strongly detected in brain and testis whereas other tissues analyzed did not appear to contain any glutamylated isoforms. Neuronal microtubules are glutamylated on α-tubulin only whereas sperm flagella showed a strong modification of both α- and ß-tubulin. These results argue for an essential role for glutamylation in differentiation processes that require microtubule stabilization.