We are undertaking a survey of Philadelphia-area hospitals for levels of radiofrequency (RF) fields in the frequency range 0.1-1000 MHz, to obtain background information related to the possible interference of radiofrequency fields with medical equipment. To date, three hospitals have been surveyed: two large center city hospitals, and a regional county hospital. Measurements were performed at 6-12 sites in each hospitals, selected to include areas in which high RF levels might be expected to exist, and at other representative sites in the hospitals. The average levels of radiofrequency signals in each of these hospitals were quite low (median value about 0.03 V/m); however sites could be identified with levels of RF fields exceeding 1-2 V/m. The maximum field strength was measured in the top floor of one hospital, near a window overlooking a paging antenna mounted on the roof of an adjacent wing.