Translational activation and repression play an important role in the spatial-temporal regulation of gene expression in embryonic development. Bicaudal-C is an RNA-binding molecule believed to function at this post-transcriptional level. Loss-of-function mutants in Drosophila affect anterior-posterior patterning because of ectopic and premature translation of the posterior determinant oskar. The Xenopus homologue of Bicaudal-C is one of the few molecules that, when microinjected ectopically, results in endoderm formation in the absence of mesoderm induction. Here we report the sequence and expression pattern of the murine and human homologues of Bicaudal-C. The human gene is located on chromosome 10q21.2. Expression analysis in mouse using in situ hybridization detects expression of Bicaudal-C not only in domains detected in Xenopus, but also in previously unreported regions. As in Xenopus, mouse Bicaudal-C mRNA is found in the growing oocyte, Hensen's node, and the developing kidney. Additionally, at later stages it is strongly expressed in the developing gut endoderm, in areas of cartilage formation, in pleuro-peritoneal membrane derivatives, in lung mesenchyme, and in the stroma of the ovary. We conclude that mouse Bicaudal-C is a maternally provided gene product that is tightly regulated during mammalian cell differentiation.