The first cell fate specification process in the Drosophila embryo, formation of the germline precursors, requires posteriorly localized germ plasm. We have cloned a gene, germ cell-less (gcl), required for germline formation. Posterior localization of the gcl messenger RNA (mRNA) requires the function of those genes essential for the localization of both nanos RNA, which specifies the abdomen, and the germ cell determinants. Mothers with reduced gcl function give rise to sterile adult progeny that lack germ cells. In embryos with reduced maternal gcl product, the germ cell precursors fail to form properly. Consistent with this phenotype, gcl protein specifically associates with those nuclei that later become the nuclei of the germ cell precursors. These observations suggest that gcl functions in the germ cell specification pathway.