The homoeobox is a 183-bp DNA sequence conserved in several Drosophila genes controlling segmentation and segment identity. Homoeobox sequences have been detected in the genome of species ranging from insects and annelids to vertebrates, and homoeobox-containing genes have been cloned from sea urchin, Xenopus, mouse and man. We have recently isolated human homoeobox-containing complementary DNA clones which represent transcripts from four different human genes. We have studied the expression of these genes in tissues of human embryos and fetuses at 5-10 weeks post-conception. Most of them appear to be expressed in a stage- and tissue-specific pattern. We report here on the genomic organization of a number of human homoeoboxes and their transcriptional organization in human placenta.