In this study, which is a continuation of a project funded by NevroNor from 2007 we are expanding our scope and trying to penetrate even deeper into mechanisms that may be of importance for brain injury in the newborn period and we are at the track of som e important mechanisms. We have been able to show that a too high oxygen concentration during newborn resuscitation is toxic even if the exposure is brief. A recent Cochrane review has calculated there is a 30% reduction in newborn mortality among newborn infants in need of resuscitation by switching from 100% oxygen to 21% oxygen.Even a brief (3-10 min) exposure of pure oxygen seems to trigger inflammatory changes in the lung, heart and even the brain of newborns. A brief exposure of oxygen to asphyxiat ed newborn infants also inflict a long lasting (4 weeks) increased oxidative stress which may influence growth and development. In hypoxic newborns exposed to oxygen 3-10 minutes at birth odds ratio for developing childhood cancer is 3-4 there is presen tly no more efficient ways to reduce childhood cancer than avoiding using pure oxygen for newborns in need of resuscitation. With the full support from EU in collaboration with the Jagiollian University in Krakow we are studying changes in the whole genom e of newborn rats exposed to standard hypoxia and reoxygenated with different oxygen concentrations, that is 21, 40, 60 and 100%.We are now also studying gene expression and DNA injury in newborn animals exposed to 100% oxygen after hypoxia. Knock out m ice of important glucosylases that are DNA protective against oxygen toxicity (base excision repair) are tested out systematically .In a large international multicenter study with support from NIH in USA we are investigating isomeres of the most importan t of these glucosylases to study the effect of oxygen toxicity in premature infants with different isomers. This represents a completely novel approach to study oxygen toxicity.