The vertebrate hindbrain develops in a segmental pattern, with distinctive groups of neurons originating from different segments. We report here that members of the Hox-2 cluster of murine homoeobox genes are expressed in segment-specific patterns in the developing hindbrain, with successive genes having boundaries at two-segment intervals. These data indicate that Hox genes specify segment phenotype, a role analogous to that of their Drosophila homologues.