We assessed the Bird T-Bird VS ventilator using a model lung constructed to standard 10651-1 of the International Standards Organization. We used different combinations of lung compliance and airway resistance to simulate normal and diseased adult and paediatric lungs. Different preset tidal volumes at various respiratory rates were delivered to the model lung and compared with the actual measured tidal volumes. The results showed that the delivered tidal volumes were within the manufacturer's specification of +/- 10% of the preset tidal volumes in normal adult and paediatric combinations of lung compliance and airway resistance. The ventilator can be powered by mains electricity supply or battery and requires only optional compressed oxygen. The ventilator is suitable for the provision of advanced ventilatory support during prolonged patient transfer.