  This paper summarizes the experience gained in the use of a carborne gamma-rayspectrometer system for mapping both natural and man-made radiation. Particular emphasis is placed on the calibration of the system for converting the gamma-ray measurements to ground concentrations of potassium, uranium and thorium and the activity of {sup 000}Cs. During the Finnish Emergency Response Exercise (Resume00), the carborne system was shown to be effective in mapping both natural and man-made radiation from {sup 000}Cs fallout and in locating radioactive sources. The application of the carborne system for mineral exploration is also demonstrated. (au). 00 refs.  The Regolith X-ray Imaging Spectrometer (REXIS) is 