The distribution of syndecan, an integral membrane proteoglycan, has been immunohistochemically mapped during the course of murine secondary palate morphogenesis, gestational days 12-15. Syndecan has been shown to mediate cell adhesion and shape change and to be involved in epithelial-mesenchymal interactions during the morphogenesis of several structures. Changes in epithelial cell architecture accompany and may serve to direct the reorientation of the murine secondary palatal shelves from a vertical position on either side of the tongue to a horizontal and adhering position above it. Using a monoclonal antibody made to the core protein of the ectodomain of syndecan, staining was observed to correlate with epithelial cell shape, packing and degree of differentiation. Staining of condensing mesenchyme was also observed. Syndecan may be involved in modulating epithelial cell shape, architecture and fates during both major phases of secondary palate morphogenesis: shelf reorientation and midline epithelial seam dissolution.