This paper presents the results of the analysis carried out of ground-based zenith measurements of atmospheric brightness temperature acquired by a dual-channel radiometer at 23.8 and 31.4 GHz at Rome, Italy, uninterruptedly during 4 years, from 1992 to 1996. The cumulative distributions of the atmospheric brightness temperature, as well as of the total water vapor and liquid water contents retrieved via the inversion of radiometric measurements, are presented and discussed. The analysis is performed for various time bases: years, months, and hours of the day, allowing indications of both design parameters and meteorological aspects. Comparison is made of the radiometric data with those calculated on the basis of long-term radiosonde profiles by means of current literature models. Model-oriented analysis is also attempted concerning the separate contributions of the two individual water phases and the possibility of deriving the status of the sky from the measured brightness temperature. ¿ 1998 American Geophysical Union