Radiometric observations have been made from aircraft with spacecraft prototype instruments to test satellite remote sensing techniques. At the same time these observations have been used to study the problem of remote sensing from aircraft because of its own particular value in providing data in the support of sub-synoptic scale meteorological experiments such as the forthcoming GARP Atlantic Tropical Experiment. This paper describes aircraft radiometric methods of obtaining clear column radiances, vertical temperature profiles, total precipitable water, and cloud heights and amounts. Questions regarding vertical resolution and accuracy specification as a function of aircraft altitudes are answered. Results obtained using observations made during June 1970 with prototype versions of the Nimbus-E ITPR aboard the NASA CV-990 are presented and discussed. It is concluded that multi-spectral radiometers aboard an aircraft can be effective meteorological observing tools.