Data on environmental levels of radio-frequency energy have been obtained for Atlanta, Boston, Miami, and Philadelphia; about 5% of the population of the United States lives within these Standard Metropolitan Statistical Areas. Data are collected at 15 to 30 sample sites within each metropolitan area. Earlier investigations led to the working hypothesis that the principal sources of environmental radio-frequency radiation are contained within the broadcast service. The frequency bands measured are the standard AM broadcast band (0.5 to 1.6 MHz), the VHF-television bands (54 to 88 and 174 to 216 MHz), the FM-radio band (88 to 108 MHz), two land-mobile bands (150 and 450 MHz), and the UHF-television band (470 to 890 MHz). Representative spectra are presented. Values of power density integrated over the frequency range from 54 to 900 MHz generally fall into the range between 0.001 and 1 μ/cm2 with most values between 0.01 and 0.1 μW/cm2.