The kidneys of infants born preterm continue to develop after birth. However, preterm infants are exposed to high oxygen levels which may impact on ongoing development. In a rodent model of oxygen exposure, the blood vessels of the kidney and the numbers of stem cells will be assessed; additionally, further stem cells will be administered in order to try and prevent any impairment. It is expected that the findings of this study will help to explain the effects of preterm birth on the kidney.