A technique for the time and frequency response measurement of clinical CO2 analysers has been established. The time and frequency response of several analyser systems has been determined. This paper presents the case for the routine measurement of the dynamic performance of such systems in the context of their application in high-frequency ventilation schemes. The importance of these measurements has been demonstrated in the comparison of older and newer systems in the sense that older systems demonstrate significant deterioration in peiformance. In the context of the use of capnographs in life-support systems, it is essential to measure and monitor the dynamic peiformance of such systems to ensure the appropriate monitoring of ventilation schemes. All of the units so far analysed cannot be used for high-frequency and/or paediatric ventilation schemes of over 80 breaths per minute.