Positive end expiratory pressure (PEEP) ventilation is a valuable method in modern critical care therapy. Nevertheless it is often necessary to take patients off the ventilator for routine physiotherapy as well as for special investigations and transport. Portable ventilators or manual bag ventilators are used during the offventilator periods. In order to keep the expiratory pressure in the therapeutic range it is desirable to have a portable PEEP valve available. This valve has to be lightweight, small, easy to use, stable and cheap. AMBU Danmark has designed such a PEEP valve which fits onto adult and pediatric Non-Return (NR) valves. The latest design is a green PVC-spring type valve with a pressure range of 0-20 cm H2O. We have evaluated this valve in the laboratory for different flows, temperature, humidity and position, and in the clinic in various situations. We found the AMBU PEEP valve to be accurate and easy to use with a stable performance meeting all requirements for emergency medical care (EMC).