We report the results of an experimental study to determine the minimum required injected power to control the output frequency of a TEA CO2laser. A CW CO2waveguide laser was used as the injection oscillator. Both the power and the frequency of the injected radiation were varied, while the TEA reasonator cavity length was adjusted to match the frequency of the injected signal. Single-longitudinal mode (SLM) TEA laser radiation was produced for injected power levels which are several orders of magnitude below those previously reported. The ratio of SLM output power to injection power exceeded 1012at the lowest levels of injected intensity.