Use of oxygen is integral part of neonatal care in treatment of respiratory diseases. Although treatment of critically ill newborns with various lung diseases has resulted in increased survival, unfortunately this often results with respiratory complications mainly in the constellation of bronchopulmonary dysplasia that leaves the child lifelong handicapped. In an attempt to explain the role of hyperoxia in bronchopulmonary dysplasia, most of literature is oriented on larger airways, but the effects of hyperoxia on most distal airways as integral part of lungs were left out. Therefore, this book provides the data to elucidate the effects of hyperoxia on airway balance, and explain the mechanisms through which oxygen exposure might lead to airway hyperreactivity. Furthermore, the book describes the effects of in vitro and in vivo L-arginine supplementation on prevention of the effects of hyperoxia on contractile and relaxation response of airway smooth muscle positioned within the lung parenchyma. The book also introduces the detailed methods employed in this investigation,which is useful for professionals in the field of physiology and molecular biology.