The ultrastructural study of fetal and newborn lungs in the intrauterine infection caused by respiratory viruses showed the virus reproduction to take place in type II alveolocytes with destructive changes in cell organelles. Each type of virus results in a certain picture of ultrastructural changes. Progressing cell organelles destruction with an intensive cytoplasm vacuolization and virion presence in the cytoplasmic matrix and on the endoplasmic network membranes is characteristic for influenza. Severe cytoplasm vacuolization with lipid formation, homogenization and condensation of membranous bodies, nuclear pyknosis are observed in parainfluenza. RS-infection is characterized by virion formation on the cytoplasmic cell membrane, numerous deformed membranous bodies, filling intercellular spaces and alveolar lumen with rough granular electron-dense material, massive release of organelles into the alveolar lumen. Edema and vacuolization of endothelium, edema and focal disappearance of basal membrane are observed in the capillary walls.