This paper examines whether the Global Positioning System radio occultation (GPS/RO) measurements of the tropopause region improve tropospheric profile retrievals from infrared and microwave radiometric measurements with the Advanced TIROS Operational Vertical Sounder (ATOVS) on current National Oceanic and Atmospheric Administration (NOAA) polar orbiting satellites and with the future high spectral resolution infrared measurements from the Cross-track Infrared Sounder (CrIS) planned for the NOAA Polar Orbiting Environmental Satellite System (NPOESS). The paper presents a simulation study wherein statistical regressions are used to infer temperature and moisture retrievals from ATOVS or CrIS brightness temperatures and GPS/RO refractivity data. The ATOVS and GPS/RO combination yields tropospheric profiles in better agreement with radiosondes than profiles inferred from either system alone; GPS/RO improves ATOVS temperature retrievals around the tropopause by 0.8 K and ATOVS tropospheric moisture retrievals by 2.5%. When the infrared measurements are improved to CrIS quality, with over 1000 spectral measurements, the addition of GPS/RO improves temperature retrieval agreement with radiosondes by 0.4 K around and above the tropopause. The paper also presents results from combining real GPS/RO (CHAMP, Challenging Minisatellite Payload) and sounder (ATOVS) data. CHAMP data are evaluated against collocated radiosonde and Numerical Weather Prediction model profiles. Using CHAMP data to establish a regression relationship, real GPS/RO data are found to improve the ATOVS temperature retrievals by 0.5 K near the tropopause.