Why are scientists excited about stem cell research, particularly embryonic stem cells? Some of the most serious and debilitating medical conditions happen because of abnormal cell division and development. By studying embryonic stem cells, scientists can better understand these diseases at a cellular level, and then develop and test new treatments and potential cures. And, because of embryonic stem cells' ability to become any tissue in the body, they offer the possibility of creating tissue for transplantation while potentially overcoming the barrier of immune rejection usually associated with organ transplants.