The human homeobox gene HOX11 has been identified at the site of a chromosomal translocation in a subset of T-cell acute leukaemias. In the mouse genome, the hox11 family consists of at least three related genes, each of which possesses a highly conserved homeobox. To assist in elucidating the roles of this gene, a homologue was studied from Drosophila melanogaster. This gene, 311, shares similar identity to all three murine family members and contains the threonine residue in helix 3 of the homeodomain characteristic of the Hox11 family. It maps to a cluster of NK-homeobox genes which function in muscle development. Gene 311 exhibits a similar temporal pattern of expression to the NK genes in this cluster. Therefore, 311 may constitute part of a homeobox cluster in which the genes are both co-ordinately regulated and functionally related.