The life cycle of parasitic protozoa of the genus Leishmania consists of two morphologically distinct forms: (1) amastigotes, the form of the parasite that resides inside macrophages of the mammalian host, which are non-motile and possess only a residual flagellum; and (2) promastigotes, the extracellular forms that live in the gut of the sandfly vector, which are highly motile and possess a single prominent flagellum. During the developmental transformation of amastigotes to promastigotes, the biosynthesis of alpha- and beta-tubulin proteins is dramatically increased, presumably to provide sufficient tubulin for synthesis and maintenance of the flagellum. We show here that the level of alpha- and beta-tubulin mRNA in Leishmania enriettii promastigotes is significantly greater than that in amastigotes, as determined by both Northern blot analysis and by in vitro translation of cellular RNA. These results show that the regulated expression of the tubulin genes is controlled at the level of mRNA accumulation in L. enriettii , by contrast with Leishmania mexicana, in which the control of gene expression has been reported to be at the level of translation.