The measurement of trace constituents in the middle atmosphere by ground-based microwave spectroscopy has emerged as an important tool for probing that region of the atmosphere. However, the vertical resolution attainable with the technique has remained somewhat ambiguous and is worthy of further study. In order to explore this question, we first applied the Backus-Gilbert inversion technique, which automatically yields quantitative estimates of the inversion spatial resolution, to this particular inverse problem. This indicated that the optimum resolution of Backus-Gilbert inversions of microwave spectroscopic measurements is about 10 km. We then developed a general technique, based on inversion of delta function simulated profiles, for evaluating the resolution of any inversion technique. This was applied to the Chahine inversion technique, which is representative of inversion methods typically used in microwave spectroscopy. These results indicated that the optimum resolution of the Chahine technique is about 6 or 7 km, or nearly a factor of 2 better than the equivalent Backus-Gilbert results. With the addition of simulated measurement error this resolution is degraded somewhat, especially near the inversion boundaries. However, for random measurement errors up to about the 1% level, 6- or 7-km resolution is still attainable in the interior of the inversion domain. ¿ American Geophysical Union 1988