Evi-1 is a putative protooncogene first identified as a common site of retroviral integration in murine myeloid leukemias. It encodes a 145×10³Af_r nuclear DNA-binding protein that contains ten zinc-finger motifs separated into two domains, as well as an acidic domain. These features suggest that Evi-1 encodes a transcriptional regulatory protein. In Drosophila, zinc-finger proteins such as Kruppel are involved in body plan patterning, and exhibit a spatially restricted pattern of expression in the embryo. To determine if Evi-1 may be involved in morphogenetic processes in the mouse embryo, we have performed in situ hybridization and Northern blot analysis on embryonic and adult mouse tissues to delineate the spatial and temporal pattern of Evi-1 expression. Our results show that Evi-1 is expressed at high levels in a few tissues in the embryo and is widely expressed, albeit at generally low levels, in the adult. Regions that exhibit high-level expression in the embryo include: the urinary system and the Mullerian ducts; the bronchial epithelium of the lung; focal areas within the nasal cavities; the endocardial cushions and truncus swellings in the heart; and the developing limbs. Expression in the limb occurs at the highest levels from 9.5 to 12.5 days, is present in both hind and forelimbs, is absent at the apical ectodermal ridge, and does not appear to establish a gradient. This pattern of expression in the limb is reminiscent of other putative transcriptional factors such as Hox-5.2 and retinoic acid receptor-gamma, consistent with the hypothesis that particular combinations or networks of transcriptional regulatory proteins are required for morphogenesis. Overall, these results suggest that Evi-1 plays an important role in mouse development.