The discovery late last year of a way to generate stem cells from adult skin cells could allow scientists to study disease in unprece­dented detail, from earliest inception to final biochemi­cal demise. That's because the stem cells could be used to develop cell lines derived from people with a given disease--neurons from Alzheimer's patients, for example, or blood cells from people with sickle-cell ­anemia. The resulting trove of cells would capture all the genetic quirks of these complex diseases.

By comparing the development and behavior of cells derived from healthy and diseased people, scientists could determine how disease unfolds at a cellular level, identifying points in the process where intervention might do some good. They could also use the cells to test drugs that might correct biochemical abnormalities. "We want to use these cells to ask and answer questions that can't be asked and answered any other way," says M. ­William Lensch, a scientist at the Harvard Stem Cell Institute.