Abstract: In a method and apparatus for the analysis of gaseous compounds, especially for determining the concentration of a gas in a gas mixture by microwave spectroscopy, pulsed microwave radiation is coupled into a resonator which is tunable to various frequencies and which is disposed in an evacuated receiver. Either air or any gas mixture including the compounds to be determined is admitted to the receiver as a pulsed molecular jet. As a result of the microwave pulse the gas compound to be determined generates an emission which is coupled out from the resonator during the intervals between the incident microwave pulses. After adjusting by mixing to frequencies in a range of preferably below 50 MHz the measured signal is digitized and analyzed possibly by Fourier analysis.