Apoptosis or programmed cell death is a genetically controlled process that eliminates harmful or unwanted cells. This process plays an important role during development by contributing to tissue sculpting and in maintaining homeostasis of cell number in a variety of tissues. Recently, we have identified a family of apoptotic inhibitory proteins, naip, hiap1 & hiap2, and xiap, which are capable of suppressing caspases, key proteolytic mediators of apoptosis. To elucidate a potential role for xiap during development, we have analyzed the expression patterns of the murine equivalent, miap3, at various stages of mouse development. In situ hybridization studies have revealed a ubiquitous expression pattern for miap3 mRNA in a variety of developing organs, including brain, heart, lung, liver, pancreas, intestines and skin. Similar results were observed with wholemount in situ hybridization. In addition, immunohistochemical analysis demonstrated that miap3 is widely expressed during embryonic days 9.5 to 16.5. Furthermore, miap3 protein expression was observed in many of the adult mouse tissues and in day 9 to 13 mouse embryos by western blot analysis. These results demonstrate that miap3 is ubiquitously distributed suggesting that it is an essential regulator of cell survival during murine development.