Expression of Ultrabithorax (UBX) proteins via a heat-inducible promoter generated homeotic transformations of segmental identities in the embryonic cuticle and peripheral nervous system (PNS) of Drosophila and transformed antennae into legs in the adult. The embryonic transformations were used to determine the identity functions of members of the UBX family and UBX mutant forms. Whereas UBX forms I and IV each induced the cuticle transformations, only form I induced the PNS transformations. Analysis of the transformations generated by UBX deletions and by a chimeric Ultrabithorax-Antennapedia protein demonstrated that the majority of the UBX identity information is contained within the C-terminal, homeodomain-containing portion of the protein. Implications of these results for how homeotic proteins select particular metameric identities are discussed.