Metabolic gas exchange and respired minute volume were measured on 37 occasions in 9 normal adults on exercise and at rest, using the concentration of an injected gas, argon, as a measure of flow. These measurements were compared with simultaneous Douglas bag collections in which volumes were determined with a dry gas meter. The two types of measurements agreed within +/- 5%. It was concluded that this technique, designed for the remote monitoring of unconscious patients was suitable for a wide variety of clinical and experimental situations.