Fipronil (Termidor) was evaluated at three concentrations (0.06%, 0.09%, and 0.125%) against structural infestations of the eastern subterranean termite, Reticulitermes flavipes, in central Ohio, where basement construction predominates. Three months after treatment, termite activity was no longer evident in any structure, although termites were found in one or more wooden monitors outside of the treated zone at three structures. At all yearly inspections, no evidence of termite activity was found indoors and all wooden monitors around the perimeter were devoid of termites. Furthermore, residents have reported the absence of termite swarmers. Data indicate that perimeter treatments using fipronil have provided protection of these structures in Ohio for 2-4 years. These field studies are ongoing.