External respiratory function was explored in 39 children aged 1.5 months to 2 years presenting with the bronchoobstructive syndrome (BOS) in the presence of acute respiratory virus infection. The development of the BOS was accompanied by disorders of bronchial patency and alveolar ventilation. The maintenance of adequate ventilation is reached at the expense of hurried breathing with the respiratory volume being lowered. During convalescence, bronchial patency rises, hyperinflation drops and the respiratory volume increases. Uniformity of the ventilation-perfusion relations in the lungs declines. The use of total body plethysmography and oxycapnography makes it possible to objectively estimate respiratory function and to control the efficacy of the treatment in infants.