In July 1997, the NASA Langley Research Center's Lidar Atmospheric Sensing Experiment (LASE) was flown on a NASA-P3 aircraft during the Southern Great Plains 1997 (SGP97) Experiment. The LASE instrument is an airborne, downward-looking differential absorption lidar system capable of measuring water vapor concentration as well as aerosol backscatter with high horizontal and vertical resolution in the atmospheric boundary layer (ABL). One of the objectives of the LASE deployment during SGP97 was to study the effect of soil moisture variations on the water vapor budget in the ABL. For a cloud-free ABL, most of the water vapor budget terms (time rate of change, horizontal advection, and vertical flux divergence) can be determined from the LASE water vapor data. The advection term requires additional information about the wind field that is provided by in situ measurements. For the flux divergence retrieval we use a flux-variance relationship based on large eddy simulations to estimate entrainment water vapor fluxes from the LASE water vapor variance profiles. In principle, surface water vapor fluxes can be retrieved using the same approach. However, in the cases studied so far the lidar data in the bottom half of the ABL were too noisy to derive meaningful surface flux estimates. Therefore, we use in situ measurements to provide surface water vapor fluxes. The difference between entrainment and surface water vapor flux divided by the ABL depth yields the averaged ABL vertical flux divergence. The ABL depth is retrieved from the lidar backscatter data by using a wavelet method to identify the characteristic drop in aerosol backscatter at the top of the ABL. We will present results of the water vapor budget retrieval for a number of cases and relate our findings to spatial variations in surface characteristics. In addition, the extensive surface and aircraft in situ measurements conducted during SGP97 will be used to validate the measurements of those budget terms derived solely from LASE data.