TheDrosophila boulegene is expressed exclusively in the male germline and encodes an RNA binding protein closely related to the mammalian fertility factors encoded by theDAZ(Deleted in Azoospermia) andDAZL(DAZ-like) genes. Mutation ofbouleblocks both meiotic divisions. Differentiation nonetheless continues, resulting in tetraploid spermatids that fail to mature into sperm. We have found that Boule localizes premeiotically to a perinucleolar region and then translocates to the cytoplasm at the onset of meiosis. We show that deletion of the Y chromosomeks-1fertility locus eliminates Boule nuclear localization, although it does not perturb entry into meiosis. Based on these observations we propose that Boule acts in the cytoplasm to regulate the stability or translation of messenger RNA encoding an essential meiotic factor.