The seven in absentia gene (sina) is required for formation of the R7 photoreceptor cell in the developing eye of Drosophila melanogaster. The sina protein contains a putative zinc finger domain and localises to the cell nucleus in Drosophila. We report here the identification of a family of genes in the mouse (designated Siah) with extensive sequence homology to Drosophila sina. The Siah genes fall into two main groups: Siah-1, which consists of four closely related members, two of which appear to be functional, and Siah-2, which contains a single functional member. The predicted Siah proteins show an unusually high degree of conservation with sina over the majority of their lengths, diverging significantly only at their amino terminal ends. The Siah-1 and Siah-2 genes are widely expressed at a low level in the embryo and adult. Analysis of Siah-2 by hybridisation histo-chemistry shows that it is expressed at a higher level in a restricted number of sites during development, including the olfactory epithelium, retina, forebrain and pro-liferating cartilage of developing bone. The striking degree of sequence homology observed between the Drosophila and murine genes implies strong conservation pressure on the Siah genes and suggests that they play a significant role in vertebrate development.