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I assume you mean research involving embryonic stem cells. The only reason is medical -- but you can explore the many different medical uses for embryonic stem cells. In addition to be used for testing of new drugs, they may also be able to alleviate or cure many different diseases. Check out these sites for details.
http://stemcells.nih.gov/info/basics/basics6.asp
http://www.sumanasinc.com/webcontent/animations/content/stemcells_scnt.html