We have used the polymerase chain reaction (PCR) to amplify, clone and sequence homologues of the Drosophila segment polarity genes engrailed (en), cubitus interruptus Dominant (ciD) and wingless (wg) from the genome of the brachiopod, Terebratulina retusa (Linnaeus). The deduced translation products of brachiopod en and ciD share high levels of sequence identity with their Drosophila homologues. The brachiopod wg-related clone is divergent from Drosophila wg, although clearly a member of the wg/Wnt gene family. These results indicate that structural diversity of Drosophila segment polarity genes has been evolutionarily conserved in a divergent, ancient and unsegmented animal phylum.