Clusters of Antennapedia-like homeobox genes have been found in Drosophila and in vertebrates (see ref. 2 for review) that show a remarkable similarity of organization and expression. Intriguingly, the order of the homeobox genes along the chromosome corresponds to the order of expression domains along the anterior-posterior axis of the animal. A large-scale screening for homeobox-containing genes in the nematode Caenorhabditis elegans did not initially reveal such clusters. But, as the C. elegans map has been further refined, a previously unmapped small contiguous set of cosmid clones (locus No. 38 in ref. 2) containing two homeobox genes,
ceh-13 (ref. 4) and
ceh-15 (
hom-2/3 in ref. 5; C. Kenyon personal communication) has now been located on chromosome III, to the left of the homeobox genes
mab-5 (ref. 6) and
ceh-11 (refs 4, 7; see figure). These four genes form a cluster of Antennapedia-like homeobox genes that appear to maintain the same anterior-posterior ordering found in flies and