In recent years, there have been a number of well-documented examples demonstrating that one cell type can be converted to another. Two such examples are the appearance of ectopic pancreas in the liver and formation of hepatic tissue in the pancreas. The conversion of liver to pancreas raises the intriguing possibility of generating insulin-producing beta cells for therapeutic transplantation into diabetics. There is now a striking addition to the growing list of pancreatic conversions: the formation of pancreatic tissue in the developing biliary system.