Sry, the mammalian Y-linked testis determining gene, is a member of a family of genes known as Sox genes, which encode transcription factors related by a DNA-binding motif termed the HMG box. Sox genes are known to have diverse roles in vertebrate differentiation and development. We report here the cloning and characterisation of one of these genes, Sox11, in mice. In addition to an N-terminal HMG box domain, the deduced SOX11 protein contains a number of highly conserved C-terminal motifs, which may function in transcriptional regulation. Expression of Sox11 in mouse embryos was prominent in the periventricular cells of the central nervous system, suggesting a role in neuronal maturation. Expression was also observed in a wide range of tissues involved in epithelial-mesenchymal interactions, suggesting an additional role in tissue modelling during development.