The homeobox gene family is divided into classes based on similarity of sequence across the homeodomain. Representative members of discrete classes are often conserved widely throughout evolution and this can extend to their genomic organisation and biological function. In this paper we report the first complete cDNA sequence of a member of the GBX class of homeobox genes, the murine gene Gbx-2. Sequence comparisons indicate that this homeodomain class is highly conserved within vertebrates. The homeodomain differs at only three positions out of 60 and these can be used to subdivide the GBX class homeodomains into 2 sub-classes.