Cell therapy means treating diseases with the body's own cells. One of the cell types most in demand for therapeutic purposes is the pancreatic β-cell. This is because diabetes is one of the major healthcare problems in the world. Diabetes can be treated by islet transplantation but the major limitation is the shortage of organ donors. To overcome the shortfall in donors, alternative sources of pancreatic β-cells must be found. Potential sources include embryonic or adult stem cells or, from existing β-cells. There is now a startling new addition to this list of therapies: the pancreatic α-cell. Thorel and colleagues recently showed that under circumstances of extreme pancreatic β-cell loss, α-cells may serve to replenish the insulin-producing compartment. This conversion of α-cells to β-cells represents an example of transdifferentiation. Understanding the molecular basis for transdifferentiation may help to enhance the generation of β-cells for the treatment of diabetes.