Since drawing the attention of scientists, ethicists, and policymakers, stem cells have not lost their place as one of the most promising yet controversial scientific discoveries of the 20th century. Scientists admit that they still know very little about how these undifferentiated pluripotent precursors work, but they're looking to develop a more sophisticated view, one that will unlock stem cells' therapeutic potential. Many regard embryonic stem cell (ESC) transplant as the ideal therapy for treating conditions such as Parkinson disease and diabetes, since they could replace malfunctioning cells, but so far the results in animal models have been mixed. Indeed, some groups have published different interpretations of seemingly similar studies.