Forty-one infants with acute viral bronchiolitis were hospitalized in our paediatric intensive care unit during the seven year period from 1980 to 1987. In 14 out of 27 evaluated patients, Respiratory Syncitial Virus (RSV) was detected in the nasal secretions. Twenty-three children required only supportive care and monitoring. Eighteen infants had to be ventilated because of respiratory failure. The major indication for mechanical ventilation was an arterial or capillary pCO2 of more than 64 mmHg; other criteria were repeated apnoea, respiratory acidosis, and clinical deterioration. In all cases the type of the mechanical ventilation was an intermittent mandatory ventilation (IMV) with flow and time cycled respirators; muscle relaxation was not required in any case. The average duration of mechanical ventilation was 40 hours. All the children recovered uneventfully. These data suggest that even the most severe cases of acute bronchiolotis can be treated successfully, and that the mortality rate of this disease entity can be reduced to zero.