Three modes of ventilation during the transport of 30 ventilator-dependent patients were compared using blood gas variables. Ten were ventilated with a manually operated, ventilation bag (group C) and ten with a tidal volume meter at the exhalation valve of the ventilation bag (group V). Another ten patients (group O) were ventilated with a portable ventilator set to the minute volume (Ve) given in ICU. Ve was measured by volumetry as described above. Blood gases were analyzed in the ICU before and at the end of transport. In group C, significant decreases occurred in arterial (p< .01) and central venous (p< .05) Pco2, as well as in central venous Po2(p< .01). Arterial (p< .05) and central venous (p< .01) pH increased. Group V showed no statistically significant changes. In group O, arterial (p< .01) and central venous (p< .05) Pco2decreased whereas arterial (p< .01) and central venous (p< .05) pH increased. We conclude that Ve should be monitored during transport of ventilated patients.