First discovered in the fungus Aspergillus nidulans, gamma-tubulin is a ubiquitous component of microtubule organizing centres . In centrosomes, gamma-tubulin has been immunolocalized at the pericentriolar material, suggesting a role in cytoplasmic microtubule nucleation , as well as within the centriole core itself . Although its function in the nucleation of the mitotic spindle and of cytoplasmic interphasic microtubules has been demonstrated in vitro   and in vivo  , the hypothesis that gamma-tubulin could intervene in centriole assembly has never been experimentally addressed because the mitotic arrest caused by the inactivation of gamma-tubulin in vivo precludes any further phenotypic analysis of putative centriole defects. The issue can be addressed in the ciliate Paramecium, which is characterized by numerous basal bodies that are similar to centrioles but the biogenesis of which is not tightly coupled to the nuclear division cycle. We demonstrate that the inactivation of the Paramecium gamma-tubulin genes leads to inhibition of basal body duplication.