In perinatal health care, respiratory distress (RDS) is a frequent life-threatening condition. The syndrome is due to a functional immaturity of the pulmonary surfactant. Our increasing understanding of the pathophysiological mecha nisms of RDS and the possibility of preventive therapeutic action have engen dered a large number of excellent articles and monographs on the perinatal development of the surfactant system with emphasis on the metabolic matura tion of the lung (6, 21-23, 26, 29, 30, 37). Therefore the aim of this article will be to describe particularly the morphology of lung development, stressing the fact that the pulmonary structure is still immature at birth.