The protein product of the Drosophila maternal-effect posterior group gene vasa is localized to the posterior pole of the oocyte and is sequestered by the pole cells as they form. It is, however, present at easily detectable levels throughout the oocyte and pre-blastoderm embryo. The protein is present in the pole cells and their germ line derivatives throughout all stages of development. An antiserum against this protein recognizes a pole-cell-specific antigen in seven other Drosophila species. Of six other maternal-effect loci essential for embryonic pole cell development, none affects expression of vasa, mutations in four abolish vasa protein localization, and mutations in two, tudor and valois, have little, if any, effect on vasa expression or localization. This indicates that vasa protein, when properly localized, is not sufficient for induction of pole cell development, and that at least the tudor and valois wild-type functions are also required specifically for this process. These results are discussed with respect to the multiple functions of the vasa gene.