The vertebrate Slug gene encodes a zinc finger-containing transcriptional repressor. Here we report expression of the mouse Slug gene during organogenesis and late fetal development using histochemical detection of β-galactosidase expressed from a targeted SluglacZ knock-in allele. The Slug gene is highly expressed in the mesenchymal or stromal component of numerous organs. It is also highly expressed in craniofacial mesenchyme, in bone of both mesodermal and neural crest origin, and in the outflow tract and the endocardial cushions of the heart. Anat Rec Part A 271A:189–191, 2003. © 2003 Wiley-Liss, Inc.