During May 1985, the Electromagnetics Branch of the Environmental Protection Agency's (EPA) Office of Radiation Programs (ORP) conducted a radiofrequency (RF) radiation investigation on Cougar Mountain, Washington. EPA found that FM radio broadcast antennas are the only significant sources of RF on Cougar Mountain. Two types of results are presented in the report, spatially averaged values and maximum localized values. The spatially averaged values are most representative of an individual's typical whole-body exposure. The maximum values are normally associated with areas of limited extent wherein only partial-body exposures might occur. The greatest spatially averaged power density measured in a publicly accessible location is 700 microwatts/sq cm within 25 feet of a tower which supports an FM antenna. Measured localized maximum power densities in two publicly accessible areas exceeded the 1,000 microwatts/sq cm ANSI radiation protection guide adopted by the FCC. Near residences, the greatest spatially averaged power density found was 117 microwatts/sq cm. Indoors, highly localized power densities reached 350 microwatts/sq cm, while spatially averaged values did not exceed 23 microwatts/sq cm.