The Drosophila genes eyeless, eyes absent, sine oculis, and dachshund cooperate as key regulators of retinal cell-fate determination. Homologues of eyeless (Pax6), eyes absent (Eya1-2), and sine oculis (Six3) have been identified and are expressed in the developing vertebrate eye. We have cloned and characterized the structure and expression of mouse Dach, a homologue of Drosophila dachshund. Sequence analysis reveals the presence of two motifs, DD1 and DD2, which may be involved in the function of Dach/Dachshund as gene regulatory factors. In addition, DD1 shares sequence similarity to N-terminal sequences of Ski and SnoN, which are involved in cellular transformation and differentiation. Mouse and human Dach/DACH were localized to chromosome 14E1 and 13q21.3-22, respectively, by fluorescence in situ hybridization. Finally, in situ hybridization analysis demonstrated that Dach is expressed in similar tissues to those observed in Drosophila, including the embryonic nervous system, sensory organs, and limbs. The finding of Dach expression in the eye completes the list of vertebrate homologues of eyeless, eyes absent, sine oculis, and dachshund which as a group may function to control cell-fate determination in the vertebrate eye.