Toxicities of 11 topically applied termiticides to the Formosan subterranean termite, Coptotermes formosanus Shiraki, and the eastern subterranean termite, Reticulitermes flavipes (Kollar) were determined. At LD50, deltamethrin was most toxic (0.12 and 0.01 μg/g for C. Formosan us and R. fiavipes , respectively), while chlordane was least toxic (LD50:45.34 and 20.10 μg/g, respectively). R. flavipes was more susceptible to all termiticides than C. formosanus . The relative susceptibility of the two termite species ( C. formosanus LD50÷ R. fiavipes LD50) ranged from 2.0 (chlorpyrifos) to 12.9 (bifenthrin). In a tunneling test in which termites were given a choice of penetrating or avoiding treated soil, all nine pyrethroids tested were repellent at sublethal doses. At appropriate concentrations, termites did not penetrate soil treated with pyrethroids and did not contact the toxicant. Significant mortality was mostly observed as termites tunneled through deposits of chlordane and chlorpyrifos and were killed by constant exposure. Soil treated with chlordane was most vulnerable to termite tunneling activity. Both termite species penetrated the 5 cm soil treated with 10 ppm of chlordane. Tunneling was inhibited with both species in soil treated with 1 ppm permethrin, while deltamethrin and cyhalothrin totally stopped tunneling by R. fiavipes at the concentrations as low as 0.4-0.8 ppm.