Based on the studies of the direct detection of electro-inactive gas CO2 by amperometry and the mechanism of oxygen interference, a new modulated potential pulse coulometry/amperometry (MPPC/MPPA), which combines the fast modulated potential technique with the microelectrode method, has been advanced and established for the rapid determination of both CO2 and O2. The influence of modulated potential-time waveforms on the electrode activity, the accuracy and range of detection was investigated. Results were obtained which demonstrate that the novel biomedical sensor techniques can be used for the non-invasive, real-time and dynamic simultaneous monitoring of respiratory gases CO2 and O2.