Abstract: The present invention relates to a method of separating pancreatic Islet cells or progenitor or stem cells thereof from a mixed population of cells from the pancreas. This involves selecting an enhancer/promoter which functions in the pancreatic Islet cells or progenitor cells thereof and introducing a nucleic acid molecule encoding a fluorescent protein under control of the enhancer/promoter into the mixed population of cells. The pancreatic Islet cells or progenitor or stem cells thereof are then allowed to express the fluorescent protein. The fluorescent cells (i.e. the said pancreatic Islet cells or progenitor or stem cells thereof) are then separated from the mixed population of cells. Also disclosed is an enriched or purified preparation of isolated human pancreatic Islet cells or progenitor or stem cells and the use of these cells in a method of treating a diabetic condition by transplanting the cells into a subject.