Three types of portable infusers with different infusion mechanisms were evaluated with regard to their accuracy during a hyperbaric oxygenation protocoL The power driving the pump is provided by either a balloon, a spring or a vacuum mechanism. Performance during hyperbaric oxygenation (HBO) varied between the devices, probably due to the difference in driving mechanism. Flow delivery by the vacuum type infuser is substantially affected by HBO. Doubling the ambient pressure approximately doubled flow delivery from the vacuum type device. We suggest that other devices are more suitable for use in this clinical situation. We conclude that it is desirable to check the performance of any infuser intended for use during hyperbaric oxygenation and to be mindful of potential differences among such devices.