/To assess how widely the type of complex regulatory region seen in mouse occurs, POU1F1 genes in a wide range of tetrapod species were investigated, identifying conserved sequences by BLAST analysis. The five-enhancer arrangement was conserved in many mammals, including marsupials, but in a number of mammalian groups one, or sometimes two enhancers are lost. In reptiles, birds and amphibia, equivalents to only three of the five enhancers seen in mouse are conserved. Elements A and D are absent in all cases examined, but Elements B, C and E are present in almost all cases, suggesting a less flexible arrangement than seen in mammals. Some variation is apparent however. In particular, in Anura (frogs and toads) the orientation of element C is reversed compared with that in other amphibians and in all other tetrapods. Furthermore, the size of the regulatory region, and spacing of elements within it exhibited considerable variability.