69 cases of respiratory diseases in children are presented and atributed to non-bacterial agents, probably viral. Using clinical and morphological criteria, a review of 372 cases of infections lung diseases was performed in autopsy material. The reaction due to the viral injury is characterized morphologically by interstitial mononuclear infiltration, mainly peribronchiolar; degenerative changes, necrosis and hyperplasia of the respiratory epithelium; hyaline membrane; epithelial desquamation; syncytial giant-cells, alveolar or bronquiolar; nuclear and cytoplasmic inclusions; proteinaceous edema, alveolar and septal; mild intersticial conective tissue proliferation. The overdiagnosis of "mononuclear intesticial pneumonia' is criticized; on the other hand, attention is called to the underdiagnosis of viral pneumonia when bacterial complication difficults its bronchiolitis for morphological diagnosis of viral disease of the lung is stressed. Those lesions - correlated the clinico-radiological and epidemiological findings - constitute which the acquired experience judge as the reaction of the lung to several known viruses (adenovirus, influenza, parainfluenza, sysncytial respiratory virus and measles).