Field bioassays were conducted to evaluate the effectiveness of different treatment combinations of permethrin-impregnated clothing and a new extended duration repellent formulation of deet against natural populations of mosquitoes in Islamabad, Pakistan. Tests were initiated 2-2 1/2 hours prior to sunset and volunteers who wore the topical repellent applied it 8 hours earlier. The most effective treatment was a combination of wearing both the permethrin-impregnated clothing and the repellent on exposed skin. This combination provided 100% protection from bites whereas volunteers wearing only treated clothing received 57% protection. Those wearing only repellent received 89% protection, but, under the biting pressure observed, this was not significantly different from the treated clothing-repellent combination.