A scanning 5-mm-wavelength (60 GHz) radiometer was deployed during two recent experiments. The first was in September-October in 1995 when the Environmental Technology Laboratory conducted the Coastal Ocean Probing Experiment off the Oregon coast. During this experiment the scanning radiometer was deployed on the Floating Instrument Platform, a research vessel operated by the Scripps Institution of Oceanography. Ground truth for the radiometer was provided by two independent in situ and infrared measurements of the ocean surface temperature; ground truth for air temperature was also provided by two in situ measurements at 0.5 and 12 m above the ocean surface. The second experiment was during September 10--30, 1996, at the Department of Energy's Atmospheric Radiation Measurement Program's Cloud and Radiation Testbed site near Lamont, Oklahoma. Here ground truth for derived quantities consisted of 3-hourly radiosonde releases and measurements at 25 and 60 m from a meteorological tower. The results of the experiments indicate that the scanning radiometer yields accuracies of the order of 0.4 ¿C rms for sea-air temperature difference and accuracies in temperature of better than 0.7 ¿C rms at altitudes below 60 m. ¿ 1998 American Geophysical Union