A microwave instrument developed for operational measurements of ozone for the Network for Detection of Stratospheric Change is discussed. The instrument observes two spectral lines near 3 mm wavelength with a bandwidth of 630 MHz, allowing profile retrieval from 20 to 70 km. The observing technique and calibration procedures are described. The measurement forward model and retrieval algorithm are formulated. Preliminary comparisons with a co-located ground-based lidar and the SAGE II instrument are presented. The measurements are shown to typically agree to within 5 to 10%. ¿ American Geophysical Union 1991