Much effort has been directed towards the investigation of regulatory processes in the early mouse embryo. Several multigene families of developmental control genes have been identified. The POU family is a group of related transcription factors containing a particular type of bipartite DNA-binding domain. Members of this family show distinct expression patterns during embryonic development. Two members, Oct-4 and Oct-6, are expressed as early as in the preimplantation embryo and thus may regulate early events of murine development.