The homoeobox is a 183 base-pair (bp) DNA sequence conserved in several Drosophila genes controlling segmentation and segment identity. Homoeobox sequences such as the Antennapedia homeodomain have been detected in the genome of species ranging from insects and anellids to vertebrates and homoeobox containing genes have been cloned from Xenopus, mouse and man. During early mammalian development homoeobox genes may exert a wide spectrum of control functions in a variety of organs and body parts, in addition to the spinal cord.