The NASA/GSFC Crustal Dynamics Project microwave water vapor radiometer (J03) is evaluated in terms of measurements of the integrated precipitable water vapor content of a particular column of the troposphere. The measurements were taken during the Atmospheric Moisture Intercomparison Study (ATMIS) held at Wallops Island, Virginia, during April 1989. Various water vapor sensing instruments were used during ATMIS, including radiometers, radiosondes, and the NASA/GSFC Raman lidar. Comparisons between water vapor measurements by the radiometer and the lidar yielded a correlation coefficient of 0.998 and rms differences for three nights of −0.2±0.2mm (April 11–12, 1989), −0.8±0.5 mm (April 16–17, 1989), and −0.4±0.3 mm (April 17–18, 1989). The integrated precipitable water vapor measurements for these three nights were approximately 5, 10, and 21 mm, respectively. The first two periods had clear meteorological conditions, while clouds were present during the third period. The lidar results during the third period are augmented with radiosonde measurements above the cloud base. This study shows that the radiometer provides accurate, continuous measurements of the water vapor integrated through the depth of