The use of microwave cavity techniques in the study of ionization in detonation waves and shock waves in reactive gas mixtures is discussed. Absorption measurements were conducted using a cavity oscillating in the TM010 mode at S band frequency and the shift in resonant frequency of a TE011 mode cavity, operating at X band frequency, was obtained by repetitively sweeping the frequency through the cavity resonance and displaying the response by means of a raster scan generator. The results are compared with microwave free-propagation experiments obtained at X and Q band frequencies in which both the microwave power absorbed by the ionized medium and the power transmitted through and reflected from the medium are monitored. Some results obtained by dc probes are also included for comparison.Equilibrium conductivities measured for the oxyhydrogen and oxyacetylene detonation waves are in reasonable accord with theoretical values. For the reactive shocks, however, the results obtained from the microwave reflection techniques yield far higher values of electron density than those obtained by the absorption methods; this is attributed to the inhomogeneous nature of the ionized medium.