Due to their similarity to human kidneys, mouse kidneys are extremely useful in scientific studies. For example, researchers have gained a much better understanding of many common forms of kidney disease by using genetically engineered mice as models. Moreover, recently a team of scientists working at the Institute of Science successfully used human stem cells to grow new organs inside of kidney deficient mice. The miniature human kidneys were fully functional and were carefully monitored in order to gauge the possibility of rejection. Further research may make it possible for humans to grow their own replacement kidneys, offering new hope to the tens of thousands of people on waiting lists for organ donations.