The FIFE Radiosonde Data Set contains temperatures, wind speed, and temperature profiles in the atmospheric boundary layer measured by means of radiosondes that were analyzed in the framework of Monin-Obukhov similarity theory, with the objective of determining the regional surface heat flux. Profiles of temperature, humidity and wind velocity in the atmosphere were measured by means of intensive radiosoundings conducted approximately between 900 and 1800 CDST in northeastern Kansas during the five FIFE Intensive Field Campaigns in spring, summer and fall of 1987, and in the late summer of 1989. Some 445 radiosondes were released to generate the measurements needed to obtain profiles of wind velocity dry-bulb and wet-bulb temperature. The launch site was located near the northern edge of the experimental area to ensure that these profiles reflect surface conditions over the fetch of the experimental area in the general direction of the prevailing southerly wind. The raw radiosonde data described here have been corrected for sensor delays (see the FIFE Temperature and Humidity Profiles) and algorithm inconsistencies, (see the FIFE Radiosonde Wind Profiles) and have been interpolated to a set of standard pressure levels (see the FIFE Standard Pressure Level Radiosonde Data). These derived data sets are described separately.