[en] Two aerial radiological surveys to measure terrestrial gamma radiation were made over an area centered on the United States Department of Energy's Feed Materials Production Center in the city of Fernald, Ohio. The Center is operated by the National Lead Company of Ohio. Gamma ray data were collected from east-west flight lines at 90 m intervals over an area 25 km² centered on the plant site. The small Ohio towns of Shandon, Ross, and New Baltimore were surveyed from north-south flight lines at 300 m intervals. Processed data indicated that on-site radioactivity was due primarily to radionuclides currently being handled or processed at the Center. Off-site data showed the radioactivity to be due to naturally occurring radionuclides northeast and south of the site. If the northwest corner of the survey area an unusually high count rate region of airborne radon daughter activity was encountered. This was equivalent to approximately four times the normal background. However, the follow-up survey of 1977 showed this area to be within the background count rate level