Thiamethoxam and fipronil were examined for their termiticidal properties against the Formosan subterranean termite, Coptotermes formosanus Shiraki, and the eastern subterranean termite, Reticulitermes flavipes (Kollar). Concentrations ≥8 ppm thiamethoxam and ≥1 ppm fipronil provided an effective barrier against C. formosanus and R. flavipes. Sand was penetrated to some degree at all concentrations of thiamethoxam (0–800 ppm for C. formosanus and 0–1,000 ppm for R. flavipes) and fipronil (0–64 ppm for both C. formosanus and R. flavipes) tested, indicating that both termiticides are nonrepellent. Thiamethoxam was found to be more toxic against C. formosanus than R. flavipes whereas fipronil showed similar toxicity for both species. Higher mortality prevented termites from penetrating the entire 5-cm segment of treated sand.